Surfactant Injury in the Early Phase of Severe Meconium Aspiration Syndrome.

No in vivo data are available regarding the effect of meconium on human surfactant in the early stages of severe meconium aspiration syndrome (MAS). In the present study, we sought to characterize the changes in surfactant composition, function, and structure during the early phase of meconium injury. We designed a translational prospective cohort study of nonbronchoscopic BAL of neonates with severe MAS (n = 14) or no lung disease (n = 18). Surfactant lipids were analyzed by liquid chromatography-high-resolution mass spectrometry. Secretory phospholipase A2 subtypes IB, V, and X and SP-A (surfactant protein A) were assayed by ELISA. SP-B and SP-C were analyzed by Western blotting under both nonreducing and reducing conditions. Surfactant function was assessed by adsorption test and captive bubble surfactometry, and lung aeration was evaluated by semiquantitative lung ultrasound. Surfactant nanostructure was studied using cryo-EM and atomic force microscopy. Several changes in phospholipid subclasses were detected during MAS. Lysophosphatidylcholine species released by phospholipase A2 hydrolysis were increased. SP-B and SP-C were significantly increased together with some shorter immature forms of SP-B. Surfactant function was impaired and correlated with poor lung aeration. Surfactant nanostructure was significantly damaged in terms of vesicle size, tridimensional complexity, and compactness. Various alterations of surfactant phospholipids and proteins were detected in the early phase of severe meconium aspiration and were due to hydrolysis and inflammation and a defensive response. This impairs both surfactant structure and function, finally resulting in reduced lung aeration. These findings support the development of new surfactant protection and antiinflammatory strategies for severe MAS.

Optimal Oxygen Targets in Term Lambs with Meconium Aspiration Syndrome and Pulmonary Hypertension.

Optimal oxygen saturation as measured by pulse oximetry (SpO2) in neonatal lung injury, such as meconium aspiration syndrome (MAS) and persistent pulmonary hypertension of newborn (PPHN), is not known. Our goal was to determine the SpO2 range in lambs with MAS and PPHN that results in the highest brain oxygen delivery (bDO2) and pulmonary blood flow (Qp) and the lowest pulmonary vascular resistance and oxidative stress. Meconium was instilled into endotracheal tubes in 25 near-term gestation lambs, and the umbilical cord was occluded to induce asphyxia and gasping, causing MAS and PPHN. Lambs were randomized into four groups and ventilated for 6 hours with fixed fraction of inspired oxygen (FiO2) = 1.0 irrespective of SpO2, and three groups had FiO2 titrated to keep preductal SpO2 between 85% and 89%, 90% and 94%, and 95% and 99%, respectively. Tissues were collected to measure nitric oxide synthase activity, 3-nitrotyrosine, and 8-isoprostanes. Throughout the 6-hour exposure period, lambs in the 95-99% SpO2 target group had the highest Qp, lowest pulmonary vascular resistance, and highest bDO2 but were exposed to higher FiO2 (0.5 ± 0.21 vs. 0.29 ± 0.17) with higher lung 3-nitrotyrosine (0.67 [interquartile range (IQR), 0.43-0.73] ng/mcg protein vs. 0.1 [IQR, 0.09-0.2] ng/mcg protein) and lower lung nitric oxide synthase activity (196 [IQR, 192-201] mMol nitrite/mg protein vs. 270 [IQR, 227-280] mMol nitrite/mg protein) compared with the 90-94% target group. Brain 3-nitrotyrosine was lower in the 85-89% target group, and brain/lung 8-isoprostane levels were not significantly different. In term lambs with MAS and PPHN, Qp and bDO2 through the first 6 hours are higher with target SpO2 in the 95-99% range. However, the 90-94% target range is associated with significantly lower FiO2 and lung oxidative stress. Clinical trials comparing the 90-94% versus the 95-99% SpO2 target range in term infants with PPHN are warranted.

Recombinant Human Superoxide Dismutase and N-Acetylcysteine Addition to Exogenous Surfactant in the Treatment of Meconium Aspiration Syndrome.

This study aimed to evaluate the molecular background of N-acetylcysteine (NAC) and recombinant human superoxide dismutase (rhSOD) antioxidant action when combined with exogenous surfactant in the treatment of meconium aspiration syndrome (MAS), considering redox signalling a principal part of cell response to meconium. Young New Zealand rabbits were instilled with meconium suspension (Mec) and treated by surfactant alone (Surf) or surfactant in combination with i.v. NAC (Surf + NAC) or i.t. rhSOD (Surf + SOD), and oxygen-ventilated for 5 h. Dynamic lung-thorax compliance, mean airway pressure, PaO2/FiO2 and ventilation efficiency index were evaluated every hour; post mortem, inflammatory and oxidative markers (advanced oxidation protein products, total antioxidant capacity, hydroxynonenal (HNE), p38 mitogen activated protein kinase, caspase 3, thromboxane, endothelin-1 and secretory phospholipase A2) were assessed in pulmonary tissue homogenates. rhSOD addition to surfactant improved significantly, but transiently, gas exchange and reduced levels of inflammatory and oxidative molecules with higher impact; Surf + NAC had stronger effect only on HNE formation, and duration of treatment efficacy in respiratory parameters. In both antioxidants, it seems that targeting reactive oxygen species may be strong supporting factor in surfactant treatment of MAS due to redox sensitivity of many intracellular pathways triggered by meconium.

Effects of Surfactant Lavage Combined With Intratracheal Budesonide Instillation on Meconium-Injured Piglet Lungs.

OBJECTIVES: To evaluate the combined effects of surfactant lavage and intratracheally instillation of budesonide on meconium-injured piglet lungs. DESIGN: A prospective, randomized, animal model study. SETTING: An experimental laboratory. SUBJECTS: Twenty-four anesthetized and mechanically ventilated newborn piglets. INTERVENTIONS: Human meconium slurry was intratracheally instilled into piglet lungs to induce lung injury. The injured piglets were randomly assigned to either the sham treatment group (control) or one of the three therapeutic groups: the intratracheally instilled budesonide (Bud) group, the bronchoalveolar lavage with diluted surfactant (dsBAL) group, and the combination therapy of Bud and dsBAL (dsBAL + Bud) group. MEASUREMENTS AND MAIN RESULTS: Cardiopulmonary profiles were measured hourly. Proinflammatory cytokine (interleukin-1ß, interleukin-6, and interleukin-8) levels in bronchoalveolar lavage fluid were measured. Finally, the pulmonary histology of the experimental subjects was examined at the end of experiments. Both of the lavaged groups (dsBAL and dsBAL + Bud) showed significantly better oxygenation than those that had not undergone lavage (control and Bud) (p < 0.05). The dsBAL + Bud group showed a significantly higher lung compliance and required a significantly lower peak inspiratory pressure during the experimental periods than the other three groups (p < 0.05). All treatment groups had significantly lower concentrations of interleukin-1ß concentration in the bronchoalveolar lavage fluid than the control group (p < 0.05). The dsBAL + Bud group also had a significantly lower interleukin-6 concentration in the bronchoalveolar lavage fluid (p< 0.05), as well as a significantly lower lung injury score based on pulmonary histology than the control group (p < 0.05). CONCLUSIONS: Therapeutic bronchoalveolar lavage with diluted surfactant followed by intratracheal instillation of budesonide has a synergistic and beneficial effect when treating severe meconium-injured newborn piglet lungs.

Antiinflammatory Effect of N-Acetylcysteine Combined with Exogenous Surfactant in Meconium-Induced Lung Injury.

Neonatal meconium aspiration syndrome (MAS) can be treated by exogenous surfactant (S). However, aspirated meconium initiates local inflammation and oxidation which may inactivate surfactant and reduce its action. This experimental study estimated whether combined use of surfactant and the antioxidant N-acetylcysteine (NAC) can enhance effectiveness of therapy. Meconium-instilled rabbits were non-treated (M), treated with monotherapies (M + S, M + NAC), combined therapy (M + S + NAC), or received saline instead of meconium (controls, C). Surfactant therapy consisted of two lung lavages (BAL) with diluted Curosurf (5 mg phospholipids/ml, 10 ml/kg) followed by undiluted Curosurf (100 mg phospholipids/kg). N-acetylcysteine (Acc Injekt, 10 mg/kg) was given intravenously in M + S + NAC group 10 min after surfactant therapy. Animals were oxygen-ventilated for additional 5 h. Then, differential white cell count in the blood (WBC) was determined. Left lung was saline-lavaged and differential cell count in BAL was determined. In right lung tissue, wet/dry weight ratio, oxidation markers (TBARS, 3NT) and interleukines (IL-2, IL-6, IL-13, and TNFα) using ELISA and RT-PCR were estimated. Combined S + NAC therapy significantly decreased W/D ratio, TBARS, 3NT, and IL, whereas the effect of monotherapies (either S or NAC) was less obvious. In conclusion, addition of NAC to surfactant treatment may enhance the therapeutic outcome in MAS.

N-acetylcysteine alleviates the meconium-induced acute lung injury.

Meconium aspiration in newborns causes lung inflammation and injury, which may lead to meconium aspiration syndrome (MAS). In this study, the effect of the antioxidant N-acetylcysteine on respiratory and inflammatory parameters were studied in a model of MAS. Oxygen-ventilated rabbits were intratracheally given 4 mL/kg of meconium (25 mg/mL) or saline. Thirty minutes later, meconium-instilled animals were administered N-acetylcysteine (10 mg/kg; i.v.), or were left without treatment. The animals were oxygen-ventilated for additional 5 h. Ventilatory pressures, oxygenation, right-to-left pulmonary shunts, and leukocyte count were measured. At the end of experiment, trachea and lung were excised. The left lung was saline-lavaged and a total and differential count of cells in bronchoalveolar lavage fluid (BAL) was determined. Right lung tissue strips were used for detection of lung edema (expressed as wet/dry weight ratio) and peroxidation (expressed by thiobarbituric acid-reactive substances, TBARS). In lung and tracheal strips, airway reactivity to acetylcholine was measured. In addition, TBARS and total antioxidant status were determined in the plasma. Meconium instillation induced polymorphonuclear-derived inflammation and oxidative stress. N-acetylcysteine improved oxygenation, reduced lung edema, decreased polymorphonuclears in BAL fluid, and diminished peroxidation and meconium-induced airway hyperreactivity compared with untreated animals. In conclusion, N-acetylcysteine effectively improved lung functions in an animal model of MAS.

The effects of pentoxifylline on lung inflammation in a rat model of meconium aspiration syndrome.

To examine the effects of pentoxifylline (PTX) on regional pulmonary and systemic inflammation after meconium aspiration, we studied 26 anesthetized and ventilated adult rats for 3 hours. Seventeen rats were instilled with human meconium (1.5 mL/kg, 65 mg/mL) intratracheally. After instillation of meconium, PTX (20 mg/kg, i.a.; n = 9) or saline (n = 8) was given to the subjects. Nine rats that were ventilated and not instilled with meconium served as sham group. Meconium instillation resulted in increased bronchoalveolar lavage (BAL) fluid tumor necrosis factor-α (TNF-α; P = 0.004 and P = 0.002, respectively), protein (P = 0.005 and P = 0.001, respectively) levels, and arterial oxygenation index (OI) in PTX and saline groups. PTX treatment prevented the increase of BAL fluid TNF-α, protein concentrations, and OI in the meconium-instilled lungs but had no statistically significant effect. These results indicate that meconium aspiration induces severe inflammation in the lung. PTX treatment affects the TNF-α production in the lungs and it may attenuate meconium-induced derangements.

Surfactant lavage decreases systemic interleukin-1 beta production in meconium aspiration syndrome.

BACKGROUND: Surfactant lavage has been used to remove meconium debris in meconium aspiration syndrome (MAS), but the influence of surfactant lavage on pro-inflammatory cytokines and cellular apoptosis is unclear. The aim of this study was to investigate the response of pro-inflammatory cytokine and the influence on alveolar cellular apoptosis using therapeutic bronchoalveolar lavage with diluted surfactant to treat MAS. METHODS: Twelve newborn piglets were anesthetized, intubated via tracheostomy, and artificially ventilated. MAS was induced by intratracheal instillation of 3-5 mL/kg of 20% human meconium. The piglets were then randomly assigned to a surfactant lavage group (n= 6) or a control group (n= 6). Piglets in the lavage group received bronchoalveolar lavage with 30 mL/kg diluted surfactant (5 mg/mL) in two aliquots. Cardiopulmonary parameters were monitored continuously. Serum was obtained hourly to measure concentrations of pro-inflammatory cytokines, including interleukin (IL)-I beta, IL-6, and tumor necrosis factor alpha. Lung tissue was histologically examined after experiments, and terminal deoxynucleotidyl transferase-mediated nick-end labeling assay for apoptotic cell death was also performed. RESULTS: The animals in the lavage group displayed significantly better gas exchange and lower serum concentrations of IL-1 beta than the animals in the control group (P < 0.05). The number of apoptotic cells in lung tissues was significantly lower in the lavage group than the control group, and also in the nondependent than the dependent site. CONCLUSION: Therapeutic surfactant lavage improves oxygenation, decreases production of systemic pro-inflammatory cytokine IL-1 beta, and alleviates the severity of lung cell apoptosis in newborn piglets with experimentally-induced MAS.

Early cardiac injury in acute respiratory distress syndrome: comparison of two experimental models.

Acute respiratory distress syndrome (ARDS) is characterized by diffuse lung damage, inflammation, oedema formation, and surfactant dysfunction leading to hypoxemia. Severe ARDS can accelerate the injury of other organs, worsening the patient´s status. There is an evidence that the lung tissue injury affects the right heart function causing cor pulmonale. However, heart tissue changes associated with ARDS are still poorly known. Therefore, this study evaluated oxidative and inflammatory modifications of the heart tissue in two experimental models of ARDS induced in New Zealand rabbits by intratracheal instillation of neonatal meconium (100 mg/kg) or by repetitive lung lavages with saline (30 ml/kg). Since induction of the respiratory insufficiency, all animals were oxygen-ventilated for next 5 h. Total and differential counts of leukocytes were measured in the arterial blood, markers of myocardial injury [(troponin, creatine kinase - myocardial band (CK-MB), lactate dehydrogenase (LD)] in the plasma, and markers of inflammation [tumour necrosis factor (TNF)alpha, interleukin (IL)-6], cardiovascular risk [galectin-3 (Gal-3)], oxidative changes [thiobarbituric acid reactive substances (TBARS), 3-nitrotyrosine (3NT)], and vascular damage [receptor for advanced glycation end products (RAGE)] in the heart tissue. Apoptosis of heart cells was investigated immunohistochemically. In both ARDS models, counts of total leukocytes and neutrophils in the blood, markers of myocardial injury, inflammation, oxidative and vascular damage in the plasma and heart tissue, and heart cell apoptosis increased compared to controls. This study indicates that changes associated with ARDS may contribute to early heart damage what can potentially deteriorate the cardiac function and contribute to its failure.

Activation of Toll-like receptors in meconium aspiration syndrome.

OBJECTIVE: Meconium aspiration syndrome (MAS) is a common cause of neonatal morbidity and mortality. Incomplete understanding of the pathogenesis of MAS has hindered the development of specific therapies. We hypothesized that activation of Toll-like receptors (TLRs) might play a role in the pathogenesis of MAS. The present study evaluated the expression of TLR 1, 4, 7, 8 and 9 in neonates with MAS. STUDY DESIGN: The study included 39 neonates with MAS and 17 healthy gestational age-matched neonates as controls. Neonates with maternal chorioamnionitis, perinatal asphyxia, sepsis and congenital malformations were excluded. Good-quality total RNA from umbilical cord blood was reverse transcribed to prepare cDNA using Bio-Rad reverse transcription kit. This cDNA was used to study the expression status of TLR 1, 4, 7, 8 and 9 by real-time quantitative polymerase chain reaction. RESULTS: Compared with controls, TLR1 and TLR4 were highly expressed, TLR9 was moderately expressed, TLR7 was weakly expressed and TLR8 expression was neutral in neonates with MAS. Within the MAS group, no difference in TLR expression was observed with respect to consistency of meconium, severity of the disease, oxygenation index and outcome. CONCLUSION: There is activation of TLRs in neonates with MAS. We speculate that these TLRs probably act as endogenous ligands for various components of meconium that initiate the inflammatory cascade of MAS and contribute to its pathogenesis.

Effects of hypothermia on lung inflammation in a rat model of meconium aspiration syndrome.

PURPOSE: To evaluate the effects of hypothermia treatment on meconium-induced inflammation. METHODS: Fifteen rats were instilled with human meconium (MEC, 1.5 mL/kg, 65 mg/mL) intratracheally and ventilated for 3 hours. Eight rats that were ventilated and not instilled with meconium served as a sham group. In MEC-hypothermia group, the body temperature was lowered to 33±0.5°C. Analysis of the blood gases, interleukin (IL)-1ß, IL-6, IL-8, and tumor necrosis factor (TNF)-α in bronchoalveolar lavage (BAL) fluid samples, and histological analyses of the lungs were performed. RESULTS: The BAL fluid TNF-α, IL-1ß, IL-6 and IL-8 concentrations were significantly higher in the MEC-hypothermia group than in the MEC-normothermia (p < 0.001, p < 0.001, p = 0.001, p < 0.001, respectively) and sham-controlled groups (p < 0.001, p < 0.001, p < 0.001, p < 0.001, respectively). CONCLUSION: Meconium-induced inflammatory cytokine production is affected by the body temperature control.

Effects of meconium on airway reactivity to histamine and acetylcholine in vitro.

To better understand the mechanisms contributing to altered airway reactivity in the meconium aspiration syndrome, in this study we investigated whether there could be a meconium dose-dependent response of tracheal smooth muscle and lung tissue reactivity to histamine and acetylcholine in vitro. Tracheal and lung tissue strips from healthy guinea pigs were incubated for 1 hour in organ chambers with three different concentrations of meconium (1, 2, and 5 mg/ml) or in Krebs-Henseleit solution. Thereafter, the contractile responses to histamine and acetylcholine were recorded. Cumulative doses of histamine and acetylcholine increased reactivity of the strips in all groups. Tracheal smooth muscle reactivity to histamine and acetylcholine (10(-5)-10(-3) mol/l) was highest with the highest meconium concentration. In contrast, lung tissue reactivity tended to decrease with increasing meconium concentration. The mechanisms influencing the airway smooth muscle contractile response to meconium require further studies.

Single-dose versus two-dose dexamethasone effects on lung inflammation and airway reactivity in meconium-instilled rabbits.

Two doses of the corticosteroid dexamethasone may alleviate meconium-induced acute lung injury more effectively than a single dose. Meconium-instilled rabbits intravenously received dexamethasone (0.5 mg/kg) at one dose 0.5 hours after meconium instillation or at two doses 0.5 hours and 2.5 hours after meconium instillation or were left without treatment, and were oxygen-ventilated for additional 5 hours. At the end of experiment, lungs and trachea were excised. Two doses of dexamethasone effectively diminished meconium-induced lung edema, tracheal hyperreactivity to histamine, neutrophil count in bronchoalveolar lavage fluid, and decreased oxidative modifications of proteins and lipids in lung homogenate compared with the non-treated group. Single-dose dexamethasone also reduced lung edema, lung neutrophils, and tracheal hyperreactivity to histamine, but these effects were weaker than those after two-dose dexamethasone. We conclude that two-dose dexamethasone is superior to single-dose dexamethasone in prevention lung injury in meconium-instilled rabbits.

Intratracheally administered corticosteroids improve lung function in meconium-instilled rabbits.

Local administration of corticosteroids may diminish acute lung injury associated with meconium aspiration. Budesonide was given intratracheally in 2 doses of 0.25 mg/kg each by means of inpulsion effect of high-frequency jet ventilation 0.5 and 2.5 hours after meconium instillation to oxygen-ventilated adult rabbits. Within 5 hours after the first dose, budesonide significantly improved gas exchange and decreased right-to-left pulmonary shunts, central venous pressure, and ventilatory pressures. In addition, budesonide reduced the meconium-induced lung edema formation, airway hyperreactivity to histamine, count of neutrophils in bronchoalveolar lavage fluid associated with higher total white blood cell and neutrophil counts in the blood, and diminished oxidative modifications of proteins and lipids in lung tissue compared to non-treated meconium-instilled group. The intratracheally administered corticosteroid budesonide effectively improved pulmonary functions and alleviated changes associated with inflammation in meconium-instilled rabbits.

Aminophylline treatment in meconium-induced acute lung injury in a rabbit model.

Administration of methylxanthines may diminish meconium-induced acute lung injury. Meconium-instilled rabbits intravenously received aminophylline (2.0 mg/kg) at two doses 0.5 h and 2.5 h after meconium instillation or were left without treatment, and were oxygen-ventilated for additional 5 h. At the end of experiment, lungs and trachea were excised. Within 5 h after the first dose of treatment, aminophylline significantly improved gas exchange and decreased right-to-left pulmonary shunts, central venous pressure, and ventilatory pressures. Moreover, aminophylline reduced meconium-induced lung edema formation, airway hyperreactivity to histamine, count of neutrophils in bronchoalveolar lavage fluid associated with higher total white blood cells and neutrophils in the blood, and diminished oxidative modifications of proteins and lipids in lung tissue compared with the non-treated meconium-instilled group. In a rabbit model of the meconium aspiration syndrome, aminophylline treatment enhanced pulmonary functions and alleviated oxidative injury and changes in airway reactivity related to lung inflammation.

Experimental models of acute lung injury in the newborns.

Acute lung injury in the preterm newborns can originate from prematurity of the lung and insufficient synthesis of pulmonary surfactant. This situation is known as respiratory distress syndrome (RDS). In the term neonates, the respiratory insufficiency is related to a secondary inactivation of the pulmonary surfactant, for instance, by action of endotoxins in bacterial pneumonia or by effects of aspirated meconium. The use of experimental models of the mentioned situations provides new information on the pathophysiology of these disorders and offers unique possibility to test novel therapeutic approaches in the conditions which are very similar to the clinical syndromes. Herewith we review the advantages and limitations of the use of experimental models of RDS and meconium aspiration syndrome (MAS) and their value for clinics.

[Regional cerebral oxygen saturation in neonates with meconium aspiration syndrome].

OBJECTIVE: This study examined the changes of regional cerebral oxygen saturation (rSO2) by noninvasive near infrared spectrophotometry in neonates with meconium aspiration syndrome (MAS). METHODS: Seventy-three full neonates with MAS were divided into three groups by respiratory symptoms: asymptomatic group (group 1, n=38), common group (group 2, n=28) and severe group (group 3, n=7). Near infrared spectrophotometry was used to measure the cerebral rSO2 on days 1, 3, 5 and 7 after birth. Thirty healthy full-term newborns served as the Control group. RESULTS: The cerebral rSO2 of group 1 decreased significantly compared with that of the Control group between days 1 and 3 (P < 0.05). The cerebral rSO2 of group 2 or group 3 was significantly lower than that of group 1 and the Control group on days 1, 3 and 5 (P < 0.05). The MAS patients with mild hypoxic-ischemic encephalopathy (HIE) had significantly higher brain rSO2 levels than those with medium or severe HIE on days 2, 3 and 5 (P < 0.05). CONCLUSIONS: The cerebral rSO2 decreased in neonates with MAS. The values for rSO2 correlated with the severity of HIE in MAS patients.

Lung inflammatory and oxidative alterations after exogenous surfactant therapy fortified with budesonide in rabbit model of meconium aspiration syndrome.

Meconium aspiration syndrome (MAS) triggers inflammatory and oxidative pathways which can inactivate both pulmonary surfactant and therapeutically given exogenous surfactant. Glucocorticoid budesonide added to exogenous surfactant can inhibit inflammation and thereby enhance treatment efficacy. Neonatal meconium (25 mg/ml, 4 ml/kg) was administered intratracheally (i.t.) to rabbits. When the MAS model was prepared, animals were treated with budesonide i.t. (Pulmicort, 0.25 mg/kg, M+B); with surfactant lung lavage (Curosurf®, 10 ml/kg, 5 mg phospholipids/ml, M+S) followed by undiluted Curosurf® i.t. (100 mg phospholipids/kg); with combination of budesonide and surfactant (M+S+B); or were untreated (M); or served as controls with saline i.t. instead of meconium (C). Animals were oxygen-ventilated for additional 5 h. Cell counts in the blood and bronchoalveolar lavage fluid (BAL), lung edema formation (wet/dry weight ratio), oxidative damage of lipids/ proteins and inflammatory expression profiles (IL-2, IL-6, IL-13, TNF-alpha) in the lung homogenate and plasma were determined. Combined surfactant+budesonide therapy was the most effective in reduction of neutrophil counts in BAL, oxidative damage, levels and mRNA expression of cytokines in the lung, and lung edema formation compared to untreated animals. Curosurf fortified with budesonide mitigated lung inflammation and oxidative modifications what indicate the perspectives of this treatment combination for MAS therapy.

Apoptosis of airway epithelial cells in response to meconium.

Meconium aspiration syndrome (MAS) is common among newborn children but its mechanism is unclear. The syndrome is known to produce a strong inflammatory reaction in the lungs resulting in massive cell death. In this work we studied lung cell death by apoptosis after meconium aspiration in forty two-week-old rabbit pups. Analyzing lung samples by ISEL-DNA end labeling demonstrated the specific spread of apoptotic bodies throughout the lungs. These bodies were shrunken and smaller in size compared to normal cells and many of them were lacking cell membranes. About 70% of all apoptotic bodies were found among the airway epithelium cell eight hours after meconium instillation. In comparison, among lung alveolar cells, only about 20% cells were apoptotic in the same animals. In meconium-treated lungs and A549 cells, a significant increase of angiotensinogen mRNA and Caspase-3 expression were observed. The pretreatment of cells with Caspase-3 inhibitor ZVAD-fmk significantly inhibited meconium-induced lung cell death by apoptosis. These findings demonstrate the apoptotic process in meconium-instilled lungs or A549 cells in culture. Our results show lung airway epithelial and A549 cell apoptosis after meconium instillation. We suggest that studies of lung airway epithelial cell death are essential to understanding the pathophysiology of MAS and may present a key point in future therapeutic applications.