Pathogenesis Of Meconium Aspiration Syndrome Research Articles

Inflammatory indices in meconium aspiration syndrome

Meconium aspiration syndrome (MAS) is linked to inflammation, but data on the patterns of hematological indices and C-reactive protein (CRP) in MAS are lacking. The aim of the study was to evaluate CRP, white blood cell count (WBC), absolute neutrophil count (ANC), and immature-to-total neutrophil ratio (IT-ratio) in MAS and to assess their association with disease severity. Retrospective cross-sectional study including 239 consecutively admitted neonates with MAS to a level III NICU. Neonates with early onset sepsis were excluded. Results Neonates with severe MAS (invasive mechanical ventilation for <7 days) and very severe MAS (invasive mechanical ventilation for ≥7 days or high frequency ventilation or ECMO) had higher CRP and IT-ratio compared to neonates with non-severe MAS (no invasive mechanical ventilation) during the first 2 days of life (CRP: 13.0 and 40.9 vs. 9.5 mg/L, P = 0.039 and <0.001, respectively) and neonates with very severe MAS had lower WBC and ANC. All four inflammatory indices correlated significantly with duration of invasive mechanical ventilation, duration of respiratory support and with length of hospital stay, arterial hypotension, and persistent pulmonary hypertension. Neonates with all four inflammatory indices beyond the normal range had a more than 20-fold increase in risk for very severe MAS. High CRP and IT-ratio and low WBC and ANC values were closely linked to a more severe course of MAS during the early phases of the disease. These findings reflect the role of inflammation in the pathogenesis of MAS. Pediatr Pulmonol. 2016;51:601-606. 2015 Wiley Periodicals, Inc.

Core Concepts: Meconium Aspiration Syndrome: Pathogenesis and Current Management

Aspiration of meconium produces a syndrome characterized by hypoxia, hypercapnia, and acidosis. Perinatal hypoxia, acute airway obstruction, pulmonary inflammation, pulmonary vasoconstriction, pulmonary hypertension, and surfactant inactivation all play a role in the pathogenesis of meconium aspiration syndrome (MAS). Most aspiration of meconium probably occurs before birth. Following aspiration, meconium can migrate to the peripheral airway, leading to airway obstruction and subsequent lung inflammation and pulmonary hypertension. The presence of meconium in the endotracheal aspirate automatically establishes the diagnosis of meconium aspiration. MAS can be diagnosed in any infant born with meconium staining of amniotic fluid who develops respiratory distress at or shortly after birth and has positive radiographic findings. Prevention of intrauterine hypoxia, early cleaning (suctioning) of the airway, and prevention and treatment of pulmonary hypertension are essential in the management of MAS. Recent studies suggest that avoidance of postterm delivery may reduce the risk of intrauterine hypoxia and the incidence of MAS. Routine intrapartum naso- and oropharyngeal suction does not appear to affect the incidence and outcome of MAS. Endotracheal suction now is reserved only for infants who are depressed or have respiratory distress at birth. Mortality of MAS has improved; the causes of death are related primarily to hypoxic respiratory failure associated with irreversible pulmonary hypertension. Morbidity is affected mostly by perinatal hypoxia.

Serum Cytokine and Chemokine Profiles in Neonates With Meconium Aspiration Syndrome

Various inflammatory cytokines and chemokines are thought to be associated with the pathophysiology of meconium aspiration syndrome. To clarify any such association, we compared various serum cytokine and chemokine profiles in patients with and without meconium aspiration syndrome. Using a highly sensitive fluorescence microsphere method, 17 types of cytokines and chemokines in sera were measured in 11 neonatal patients with meconium aspiration syndrome, 16 neonatal patients without meconium aspiration syndrome, and 9 healthy children. The concentrations of 8 types of proinflammatory cytokines and chemokines were significantly higher in the meconium aspiration syndrome group than in healthy controls: interleukin-1beta, interleukin-6, interleukin-8, granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, interferon-gamma, macrophage inflammatory protein-1beta, and tumor necrosis factor-alpha. Six types of proinflammatory cytokines and chemokines were significantly higher in the meconium aspiration syndrome group than in the nonmeconium aspiration syndrome group: interleukin-6, interleukin-8, granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, interferon-gamma, and tumor necrosis factor-alpha. Serum concentrations of interleukin-10 (anti-inflammatory cytokine) in the meconium aspiration syndrome group were higher than those in both the nonmeconium aspiration syndrome group and healthy children group (P = .007 and 0.001, respectively). Most types of proinflammatory cytokines and chemokines in sera of neonates with meconium aspiration syndrome were higher than those without meconium aspiration syndrome, giving support to the suggestion that elevated levels are associated with the pathogenesis of meconium aspiration syndrome.

Inflammation in Meconium Aspiration Syndrome: Targets for Pharmacological Modulation

Pathophysiology of meconium aspiration syndrome (MAS) is complex and interactions between individual pathomechanisms are still not completely understood. As recently shown, inflammation plays a significant role in the pathogenesis of MAS. Activated cells release and stimulate production of a wide variety of mediators, including cytokines, enzymes, reactive species, and other biologically active substances in meconium-injured lungs. Anti-inflammatory drugs acting on different levels of inflammatory cascade may in combination with other treatment (exogenous surfactant, inhaled NO, liquid ventilation) improve the clinical status of newborns with MAS. For example, corticosteroids modulate activity of phospholipase A2 and induced NO synthase, influence migration and activation of leukocytes, and reduce lung edema. Cyclooxygenase inhibitors modulate production of thromboxane and prostaglandins. Phosphodiesterase inhibitors have vasodilating, bronchodilating and anti-inflammatory effects. Antioxidants diminish formation of reactive species. However, there are many other drugs., e.g. anti-cytokine antibodies, inhibitors of complement, inhibitors of angiotensinconverting enzyme, anticoagulants, inhibitors of proteolytic enzymes, calcium-channel blockers etc. that may be beneficial in MAS. Nevertheless, further testing is necessary until the novel approaches may be recommended. In this article, authors reviewed main factors participating in meconium-induced inflammation and pointed out some targets for its pharmacological modulation. Keywords: Acute lung injury, inflammation, meconium aspiration syndrome, anti-inflammatory treatment

Pancreatic Phospholipase A2 Contributes to Lung Injury in Experimental Meconium Aspiration

To investigate the role of pancreatic (group I) secretory PLA2 (sPLA2-I) in the pathogenesis of meconium aspiration syndrome, human particulate meconium or its supernatant either before or after extraction of PLA2-I was insufflated into rat lungs. In addition, the pulmonary effects of intra-tracheal human and bovine PLA2-I were studied. Lungs with saline instillation served as controls. Intrapulmonary particulate meconium (both before and after PLA2-I extraction), unlike meconium supernatant, resulted in markedly elevated lung tissue PLA2 catalytic activity and human PLA2-I concentrations when compared with controls. On the other hand, tissue concentrations of the group II PLA2 remained unchanged in all meconium lungs. Pulmonary PLA2-I concentrations further correlated positively with lung injury scores. Instillation of meconium-derived human PLA2-I, at a concentration of one-third of that in particulate meconium, did not raise PLA2 activity or concentrations of PLA2-I or PLA2-II in the lung tissue from the control level, but still resulted in significantly elevated lung wet/dry ratio and injury score. In contrast, insufflation of bovine pancreatic PLA2 increased the lung tissue enzyme activity and wet/dry ratio from the control level, but had no effect on the type II PLA2 concentration or lung injury score. Our data thus indicate that human pancreatic PLA2, introduced in high amounts within aspirated meconium especially in particulate form, is a potent inducer of lung tissue inflammatory injury.

Meconium Is a Potent Activator of Complement in Human Serum and in Piglets

Meconium aspiration syndrome (MAS) is a clinical condition in the newborn infant with a significant morbidity and mortality. The complex pathophysiology of MAS, leading to both pulmonary and systemic complications, is characterized by an incompletely understood inflammatory reaction. Treatment is symptomatic, mainly limited to airway cleaning and ventilatory support. In this study, we show for the first time that meconium is a potent activator of complement, a key mediator of inflammation. In vitro, meconium activated the alternative complement pathway in human umbilical cord serum as judged by a substantial increase in the alternative pathway convertase C3bBbP. The activation proceeded through C3 (C3bc) and the terminal C5-9 pathway (terminal SC5b-9 complement complex), whereas the classical and lectin pathways were not activated (C1rs-C1-inhibitor complexes and C4bc). The lipid fraction, containing, e.g. free fatty acids, and the water fraction, containing, e.g. bile acids, contributed equally to the complement activation. A blocking antibody to factor D (alternative pathway) completely inhibited the meconium-induced complement activation, whereas blocking antibodies to mannose-binding lectin (lectin pathway) and C2 (classical and lectin pathway) had no effect. In vivo, meconium induced systemic complement activation in a piglet model of MAS, paralleling the increase in lung dysfunction. In conclusion, meconium is a potent activator of the complement system both in vitro and in vivo. Complement may be important in the pathogenesis of MAS, and specific complement inhibition might be a possible treatment approach in MAS.

Comparison of Pulmonary and Inflammatory Effects of Lipid- and Water-Soluble Components in Meconium in Newborn Piglets

To understand the pathogenesis of meconium aspiration syndrome, we compared the pulmonary and inflammatory effects of the water and lipid extracts of human meconium instilled into the lungs of newborn piglets. The piglets were artificially ventilated, made hypoxemic, and randomized into three groups. At start of reoxygenation, 3 ml/kg of one of the following mixtures was instilled intratracheally: (1) meconium (n = 12); (2) water extract of meconium (n = 12), and (3) lipid extract of meconium (n = 12). During 8 h of reoxygenation, hemodynamics, pulmonary gas exchange, lung mechanics, and interleukin-8 concentrations in tracheobronchial aspirates were monitored. Oxygenation index (p = 0.04) and mean airway pressure (p = 0.04) increased more in the lipid extract group than in the water extract group. Dynamic compliance and mean arterial blood pressure decreased (p < 0.05) in the meconium and lipid extract groups, but not in the water extract group. At 8 h of reoxygenation, the interleukin-8 concentration in the tracheobronchial aspirates was three times higher in the lipid extract group as compared with the water extract group (110 ± 102 vs. 37 ± 27 pg/ml; p = 0.02). In conclusion, pulmonary dysfunction in meconium aspiration syndrome is caused by both the water- and lipid-soluble fractions of meconium, with stronger inflammatory and more detrimental effects promoted by the lipid extract than the water extract.

Meconium is a source of pro-inflammatory substances and can induce cytokine production in cultured A549 epithelial cells.

Inflammation plays an important role in the pathogenesis of meconium aspiration syndrome, and pneumonitis is one of the major characteristics. We have previously shown that meconium has chemotactic properties because of the presence of IL-8. We hypothesize that IL-8 and other proinflammatory substances in meconium may amplify inflammation in meconium aspiration syndrome, inducing endogenous cytokine production by lung epithelial cells. We measured proinflammatory substances in first-pass meconium from healthy newborns and evaluated the effect of sterile meconium on cytokine production in cultured A549 alveolar epithelial cells in vitro. IL-1beta, IL-6, IL-8, and tumor necrosis factor-alpha were measured by ELISA, and heme was measured spectrophotometrically. After incubation of meconium samples with A549 cells, cytokine concentrations in the supernatant were measured. Meconium samples contained variable amounts of IL-1beta, IL-6, IL-8, tumor necrosis factor-alpha, and heme. On stimulation of A549 cells with meconium, the IL-8 concentration in the culture supernatant significantly increased above baseline measurements, whereas tumor necrosis factor-alpha showed a variable pattern and IL-1beta or IL-6 remained unchanged. There was no quantitative relationship between the concentration of the measured cytokines and heme in meconium and cytokine release by the A549 cells after meconium exposure. Meconium contains proinflammatory substances. All samples induced IL-8 release and some induced tumor necrosis factor-alpha release in cultured A549 epithelial cells. We speculate that proinflammatory substances in meconium can induce lung inflammation in meconium aspiration syndrome in two ways: directly via cytokines and heme present in meconium and indirectly by inducing cytokine release by the epithelial lung cells.

Meconium Induces Only Localized Inflammatory Lung Injury in Piglets

Neonatal meconium aspiration often produces severe respiratory distress due to an inflammatory pulmonary injury, but the extension of this damaging reaction to the noncontaminated lung regions is still uncertain. To investigate the presence of generalized pulmonary inflammatory response, 31 anesthetized and ventilated neonatal piglets (1-3 d) were studied. Meconium (n = 16) or saline (n = 15) was instilled unilaterally into the right lung, and analysis of the lung tissue or bronchoalveolar lavage (BAL) fluid from both lungs was performed after 12 h. Meconium increased the wet/dry weight ratio, histologic tissue injury score and tissue myeloperoxidase activity as well as BAL fluid total cell count in the contaminated lung. Tumor necrosis factor-alfa concentrations in BAL fluid did not however differ significantly. Furthermore, in the meconium-instilled lungs the tissue and lavage fluid catalytic activity of phospholipase A2 (PLA2) and tissue PLA2 group-I and group-II concentrations were significantly elevated. Although BAL fluid catalytic activity of PLA2 was moderately increased also in the meconium noninstilled lung, significant inflammatory injury in this lung was absent. The results thus indicate that meconium aspiration induces severe local inflammation and lung injury, but significant generalized pulmonary inflammatory damage in the pathogenesis of meconium aspiration syndrome is unlikely.

Meconium Enhances the Release of Nitric Oxide in Human Airway Epithelial Cells

Meconium aspiration syndrome (MAS) is a cause of significant morbidity and mortality in the perinatal period. Despite the clinical relevance of MAS, its pathogenesis is poorly understood and the role played by epithelial-derived metabolites not well defined. In this study, we evaluated whether exposure to meconium affects the release of nitric oxide production in human airway epithelial cells. Monolayers of A549 cells, a transformed human epithelial cell line, were incubated with various concentrations of meconium. Control cells were incubated with serum-free medium in a similar manner. The supernatant fluid was removed at various time points and assayed for nitrite production. In selected experiments, the effects of dexamethasone (10^–6 M), L-nitroarginine methyl ester (L-NAME, 10^–6 M) and indomethacin (10^–6 M) on nitrite release were evaluated. Results were obtained in terms of pmol/mg protein and expressed as % control (mean ± SE). We found exposure to meconium produced a significant release of nitrite from A549 cells. Dexamethasone, L-NAME and indomethacin inhibited meconium-induced release of nitrite. Our findings demonstrate meconium enhances the production of nitric oxide from A549 cells suggesting that airway epithelial cells and their metabolic products may play an important role in the pathogenesis of MAS.

Meconium-induced lung injury mediated by activation of alveolar macrophages

To clarify the mechanism of meconium-induced cellular injury, we examined the effect of meconium on the alveolar macrophages (AM) and bronchial epithelial cells (AK-D). Meconium obtained from healthy newborns was added to culture medium of AM and/or AK-D, which were cultured for 1 hour. Superoxide anion production of AM and the expression of intercellular adhesion molecule-1 (ICAM-1) on AK-D stimulated by meconium or oxygen radicals were determined. As a result, superoxide anion production of AM significantly increased when AM was cultured with meconium. Expression of ICAM-1 on AK-D appeared when AK-D was stimulated by hydroxyl radical but did not when AK-D was cultured with meconium. These results suggest that meconium-induced lung injury may occur through an activation of alveolar macrophages and the macrophage-epithelial cell axis may be important for the pathogenesis of meconium aspiration syndrome.