Complement activation reflects severity of meconium aspiration syndrome in newborn pigs

No Short-Term Effect of Low-Dose Nicotine on Inflammation after Global Hypoxia in Newborn Piglets

INTRODUCTION

Perinatal asphyxia initiates cytokine release and complement activation with risk of brain damage. We assessed the effect of nicotine on innate immunity and hypothesized that nicotine infusion in a newborn piglet model of asphyxia would decrease the immune response and be neuroprotective.

METHODS

Newborn piglets (n = 41) were randomized to one of three groups after hypoxia: two groups receiving nicotine, (1) 18 µg/kg/h (n = 17), (2) 46 µg/kg/h (n = 15), and (3) control group receiving saline (n = 9). C3a, IL-6, TNF, and IL-10 were measured in plasma and IL-6 and IL-8 in microdialysis fluid from cerebral periventricular white matter, using immuno-assays.

RESULTS

Plasma C3a and IL-6 increased significantly from start to end hypoxia (mean 4.4 ± 0.55 to 5.6 ± 0.71 ng/mL and 1.66 ± 1.04 to 2.68 ± 0.71 pg/mL, respectively), while IL-10 and TNF increased significantly after 4 h (mean 1.4 ± 1.08 to 2.9 ± 1.87 and 3.3 ± 0.67 to 4.0 ± 0.58 pg/mL, respectively) (p < 0.001 for all). IL-6 increased significantly (p < 0.001) in microdialysis samples from end hypoxia to end experiment (mean 0.65 ± 0.88 to 2.78 ± 1.84 ng/mL). No significant differences were observed between the nicotine groups and the control group neither in plasma nor in microdialysis samples.

CONCLUSION

Hypoxia leads to rapid release of cytokines in plasma and cerebral microdialysis fluid, and complement activation measured on C3a. However, low-dose nicotine administration did not affect the immune response.

Meconium Aspiration Syndrome in Animal Models: Inflammatory Process, Apoptosis, and Surfactant Inactivation

Meconium Aspiration Syndrome is a condition that causes respiratory distress in newborns due to occlusion and airway inflammation, and surfactant inactivation by meconium. This condition has been described in animal species such as canids, sheep, cattle, horses, pigs, and marine mammals. In its pathogenesis, the pulmonary epithelium activates a limited inflammatory response initiated by cytokines causing leukocyte chemotaxis, inhibition of phagocytosis, and pathogen destruction. Likewise, cytokines release participates in the apoptosis processes of pneumocytes due to the interaction of angiotensin with cytokines and the caspase pathway. Due to these reactions, the prevalent signs are lung injury, hypoxia, acidosis, and pneumonia with susceptibility to infection. Given the importance of the pathophysiological mechanism of meconium aspiration syndrome, this review aims to discuss the relevance of the syndrome in veterinary medicine. The inflammatory processes caused by meconium aspiration in animal models will be analyzed, and the cellular apoptosis and biochemical processes of pulmonary surfactant inactivation will be discussed.

An Unsettled Promise: The Newborn Piglet Model of Neonatal Acute Respiratory Distress Syndrome (NARDS). Physiologic Data and Systematic Review

Despite great advances in mechanical ventilation and surfactant administration for the newborn infant with life-threatening respiratory failure no specific therapies are currently established to tackle major pro-inflammatory pathways. The susceptibility of the newborn infant with neonatal acute respiratory distress syndrome (NARDS) to exogenous surfactant is linked with a suppression of most of the immunologic responses by the innate immune system, however, additional corticosteroids applied in any severe pediatric lung disease with inflammatory background do not reduce morbidity or mortality and may even cause harm. Thus, the neonatal piglet model of acute lung injury serves as an excellent model to study respiratory failure and is the preferred animal model for reasons of availability, body size, similarities of porcine and human lung, robustness, and costs. In addition, similarities to the human toll-like receptor 4, the existence of intraalveolar macrophages, the sensitivity to lipopolysaccharide, and the production of nitric oxide make the piglet indispensable in anti-inflammatory research. Here we present the physiologic and immunologic data of newborn piglets from three trials involving acute lung injury secondary to repeated airway lavage (and others), mechanical ventilation, and a specific anti-inflammatory intervention via the intratracheal route using surfactant as a carrier substance. The physiologic data from many organ systems of the newborn piglet—but with preference on the lung—are presented here differentiating between baseline data from the uninjured piglet, the impact of acute lung injury on various parameters (24 h), and the follow up data after 72 h of mechanical ventilation. Data from the control group and the intervention groups are listed separately or combined. A systematic review of the newborn piglet meconium aspiration model and the repeated airway lavage model is finally presented. While many studies assessed lung injury scores, leukocyte infiltration, and protein/cytokine concentrations in bronchoalveolar fluid, a systematic approach to tackle major upstream pro-inflammatory pathways of the innate immune system is still in the fledgling stages. For the sake of newborn infants with life-threatening NARDS the newborn piglet model still is an unsettled promise offering many options to conquer neonatal physiology/immunology and to establish potent treatment modalities.

Combined Inhibition of C5 and CD14 Attenuates Systemic Inflammation in a Piglet Model of Meconium Aspiration Syndrome

BACKGROUND

Meconium aspiration syndrome (MAS) is a severe lung condition affecting newborns and it can lead to a systemic inflammatory response. We previously documented complement activation and cytokine release in a piglet MAS model. Additionally, we showed ex vivo that meconium-induced inflammation was dependent on complement and Toll-like receptors.

OBJECTIVES

To assess the efficacy of the combined inhibition of complement (C5) and CD14 on systemic inflammation induced in a forceful piglet MAS model.

METHODS

Thirty piglets were randomly allocated to a treatment group receiving the C5-inhibitor SOBI002 and anti-CD14 (n = 15) and a nontreated control group (n = 15). MAS was induced by intratracheal meconium instillation, and the piglets were observed for 5 h. Complement, cytokines, and myeloperoxidase (MPO) were measured by ELISA.

RESULTS

SOBI002 ablated C5 activity and the formation of the terminal complement complex in vivo. The combined inhibition attenuated the inflammasome cytokines IL-1β and IL-6 by 60 (p = 0.029) and 44% (p = 0.01), respectively, and also MPO activity in the bronchoalveolar fluid by 42% (p = 0.017). Ex vivo experiments in human blood revealed that the combined regimen attenuated meconium-induced MPO release by 64% (p = 0.008), but there was only a negligible effect with single inhibition, indicating a synergic cross-talk between the key molecules C5 and CD14.

CONCLUSION

Combined inhibition of C5 and CD14 attenuates meconium-induced inflammation in vivo and this could become a future therapeutic regimen for MAS.

Inflammatory indices in meconium aspiration syndrome

INTRODUCTION

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.

METHODS

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.

CONCLUSION

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.

Meconium-induced inflammation and surfactant inactivation: specifics of molecular mechanisms

This review summarizes neonatal meconium aspiration syndrome in light of meconium-induced inflammation and inflammatory surfactant inactivation, related to both endogenous and therapeutic exogenous surfactant. The wide effect of meconium on surfactant properties is divided into three points. Direct effect of meconium on surfactant properties refers mainly to fragmentation of dipalmitoylphosphatidylcholine and other surfactant phospholipids together with cleavage of surfactant proteins. Initiation of inflammatory response due to activation of receptors by yet unspecified compounds involves complement and Toll-like receptor activation. A possible role of lung collectins, surfactant proteins A and D, which can exert both pro- and anti-inflammatory reactions, is discussed. Initiation of inflammatory response by specified compounds in meconium reflects inflammatory functioning of cytokines, bile acids, and phospholipases contained in meconium. Unifying sketch of many interconnections in all these actions aims at providing integrated picture of inflammatory surfactant inactivation.

Meconium aspiration syndrome: possible pathophysiological mechanisms and future potential therapies

Does meconium cause meconium aspiration syndrome (MAS) or is meconium discharge only a marker of fetal hypoxia? This dispute has lasted for centuries, but since the 1960s, detrimental effects of meconium itself on the lungs have been demonstrated in animal experiments. In clinical MAS, persistent pulmonary hypertension of the newborn is the leading cause of death in MAS. Regarding the complex chemical composition of meconium, it is difficult to identify a single agent responsible for the pathophysiology. However, considering that meconium is stored in the intestines, partly unexposed to the immune system, aspirated meconium could be recognized as ‘danger', representing damaged self. The common denominator in the pathophysiology could therefore be activation of innate immunity. Thus, a bulk of evidence implies that meconium is a potent activator of inflammatory mediators, including cytokines, complement, prostaglandins and reactive oxygen species. We hypothesize that the two main recognition systems of innate immunity, the Toll-like receptors and the complement system, recognize meconium as ‘danger', which leads not only to lung dysfunction but also to a systemic inflammatory response. This might have therapeutic implications in the future.

Secreted phospholipase A2 is increased in meconium-stained amniotic fluid of term gestations: potential implications for the genesis of meconium aspiration syndrome

BACKGROUND

Meconium-stained amniotic fluid (MSAF) represents the passage of fetal colonic content into the amniotic cavity. Meconium aspiration syndrome (MAS) is a complication that occurs in a subset of infants with MSAF. Secreted phospholipase A2 (sPLA2) is detected in meconium and is implicated in the development of MAS. The purpose of this study was to determine if sPLA2 concentrations are increased in the amniotic fluid of women in spontaneous labor at term with MSAF.

MATERIALS AND METHODS

This was a cross-sectional study of patients in spontaneous term labor who underwent amniocentesis (n = 101). The patients were divided into two study groups: (1) MSAF (n = 61) and (2) clear fluid (n = 40). The presence of bacteria and endotoxin as well as interleukin-6 (IL-6) and sPLA2 concentrations in the amniotic fluid were determined. Statistical analyses were performed to test for normality and bivariate analysis. The Spearman correlation coefficient was used to study the relationship between sPLA2 and IL-6 concentrations in the amniotic fluid.

RESULTS

Patients with MSAF have a higher median sPLA2 concentration (ng/mL) in amniotic fluid than those with clear fluid [1.7 (0.98-2.89) versus 0.3 (0-0.6), p < 0.001]. Among patients with MSAF, those with either microbial invasion of the amniotic cavity (MIAC, defined as presence of bacteria in the amniotic cavity), or bacterial endotoxin had a significantly higher median sPLA2 concentration (ng/mL) in amniotic fluid than those without MIAC or endotoxin [2.4 (1.7-6.0) versus 1.7 (1.3-2.5), p < 0.05]. There was a positive correlation between sPLA2 and IL-6 concentrations in the amniotic fluid (Spearman Rho = 0.3, p < 0.05).

CONCLUSION

MSAF that contains bacteria or endotoxin has a higher concentration of sPLA2, and this may contribute to induce lung inflammation when meconium is aspirated before birth.

Bacteria and endotoxin in meconium-stained amniotic fluid at term: could intra-amniotic infection cause meconium passage?

BACKGROUND

Meconium-stained amniotic fluid (MSAF) is a common occurrence among women in spontaneous labor at term, and has been associated with adverse outcomes in both mother and neonate. MSAF is a risk factor for microbial invasion of the amniotic cavity (MIAC) and preterm birth among women with preterm labor and intact membranes. We now report the frequency of MIAC and the presence of bacterial endotoxin in the amniotic fluid of patients with MSAF at term.

MATERIALS AND METHODS

We conducted a cross-sectional study including women in presumed preterm labor because of uncertain dates who underwent amniocentesis, and were later determined to be at term (n = 108). Patients were allocated into two groups: (1) MSAF (n = 66) and (2) clear amniotic fluid (n = 42). The presence of bacteria was determined by microbiologic techniques, and endotoxin was detected using the Limulus amebocyte lysate (LAL) gel clot assay. Statistical analyses were performed to test for normality and bivariate comparisons.

RESULTS

Bacteria were more frequently present in patients with MSAF compared to those with clear amniotic fluid [19.6% (13/66) versus 4.7% (2/42); p < 0.05]. The microorganisms were Gram-negative rods (n = 7), Ureaplasma urealyticum (n = 4), Gram-positive rods (n = 2) and Mycoplasma hominis (n = 1). The LAL gel clot assay was positive in 46.9% (31/66) of patients with MSAF, and in 4.7% (2/42) of those with clear amniotic fluid (p < 0.001). After heat treatment, the frequency of a positive LAL gel clot assay remained higher in the MSAF group [18.1% (12/66) versus 2.3% (1/42), p < 0.05]. Median amniotic fluid IL-6 concentration (ng/mL) was higher [1.3 (0.7-1.9) versus 0.6 (0.3-1.2), p = 0.04], and median amniotic fluid glucose concentration (mg/dL) was lower [6 (0-8.9) versus 9 (7.4-12.6), p < 0.001] in the MSAF group, than in those with clear amniotic fluid.

CONCLUSION

MSAF at term was associated with an increased incidence of MIAC. The index of suspicion for an infection-related process in postpartum women and their neonates should be increased in the presence of MSAF.

Right-to-left shunting in the ductus arteriosus is induced readily by intense crying and rapid postural change in neonates with meconium-stained amniotic fluid

OBJECTIVE

To investigate postnatal changes in the direction of blood flow through the ductus arteriosus in neonates with meconium-stained amniotic fluid, we measured preductal and postductal oxygen saturation in normal neonates, neonates with meconium-stained amniotic fluid, and a neonate with persistent pulmonary hypertension of the newborn.

DESIGN

Prospective, observational case series report.

SETTING

A single, tertiary neonatal intensive care unit.

PATIENTS

Twelve normal neonates, seven neonates with meconium-stained amniotic fluid, and a neonate with persistent pulmonary hypertension of the newborn.

INTERVENTIONS

SpO2 is simultaneously monitored in the right upper and lower limbs after birth.

MEASUREMENTS AND MAIN RESULTS

Compared with normal neonates, three neonates with meconium-stained amniotic fluid required longer than +2 SD of the mean time for the postductal SpO2 to reach 90% and/or 95%. In a neonate with meconium-stained amniotic fluid, intense crying triggered frequent decreases to <70% in the postductal SpO2 from 25 mins after birth, while the preductal SpO2 remained at 95% or above. When the other newborn with meconium-stained amniotic fluid was held in the father's arms after 98 mins, the postductal SpO2 decreased rapidly to <80%, while the preductal SpO2 remained at 95%. Thus, 5% or greater difference between the preductal and postductal SpO2 was observed from 25 mins after birth until 120 mins in all neonates with meconium-stained amniotic fluid, whereas the difference disappeared after 25 mins in 12 normal neonates. In a neonate with persistent pulmonary hypertension of the newborn who required vigorous resuscitation, 5% or greater difference between the preductal and postductal SpO2 levels was observed until 6 hrs after birth.

CONCLUSIONS

Right-to-left shunting in the ductus arteriosus may be induced readily by intense crying and rapid postural change in infants with meconium-stained amniotic fluid. It is important to monitor SpO2 at both pre- and postductal regions until 120 mins after birth in neonates with meconium-stained amniotic fluid and to subject these infants to minimal manipulations.

Advances in assay of complement function and activation

The main function of the complement system is pattern recognition of danger. Typical exogenous danger signals are pathogen associated molecular patterns inducing a protective inflammatory response. Other examples are exposure to foreign surfaces of biomedical materials including nanoparticles, which principally induce the same inflammatory response. If a surface is "foreign" to the host, it induces complement activation. Development of monoclonal antibodies to neoepitopes on complement activation products introduced an entirely new set of methods for assay of complement activation. Activation of complement by a surface occurs by impairment of the fine balance of the control system, e.g. by preferred binding of factor B at the expense of factor H. Sensitive methods to detect complement activation on surfaces and in the fluid phase are a prerequisite for investigation of the biocompatibility of artificial materials. This information can be used to develop new materials with enhanced biocompatibility. Here we review available methods to study human and animal complement function and activation in vitro and in vivo.

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.

Why does meconium cause meconium aspiration syndrome? Current concepts of MAS pathophysiology

One in every 7 pregnancies ends with meconium-stained amniotic fluid and approximately 5% of these infants develop the meconium aspiration syndrome (MAS). MAS is a severe disease of the (mainly) term neonate, characterized by respiratory distress, pulmonary inflammation, persistent pulmonary hypertension and chronic hypoxia. The pathophysiology of MAS is multifactorial and complex. In this article, we discuss the mechanical and chemical effects of meconium on a newborn's airway, meconium-induced inflammation, mediated by proinflammatory cytokines and chemokines, the complement system and the proinflammatory enzyme phospholipase A2. Furthermore, we focus on MAS-related apoptotic cell death, causing severe acute lung injury due to damage and detachment of lung airway and alveolar cells. Finally, risk factors for MAS development to identify those newborns that develop MAS and those who do not are discussed.

Pathway-specific complement activity in pigs evaluated with a human functional complement assay

BACKGROUND

The complement system is an important part of innate immunity. Complement deficiencies or inappropriate activation of complement may cause severe diseases. The complement functional test, Wielisa, assesses all three complement activation pathways in humans. It is important to have assays available to determine the functional complement activity in research animals. Since the pig is a relevant animal in experimental research, the aim of the present study was to evaluate the applicability of this human complement assay in pigs.

METHODS

Normal pig serum was serially diluted and assayed in the Wielisa test which is based on the activation of complement detected with an antibody against activated C9. The specificity of the three pathways was assessed using purified human MBL and mouse monoclonal antibodies against human C1q and pig factor D. Sera from 103 pigs and 38 newborn pigs were analyzed. Finally, functional activity of all pathways was assessed in vitro and in vivo in the absence and presence of complement inhibitors.

RESULTS

The detection antibody showed cross-reactivity against pig. Normal pig serum showed activity in all pathways however about 10-fold more serum was required to obtain values comparable to human serum. Anti-human C1q and anti-pig factor D antibodies abolished classical and alternative pathway activity, respectively. Sera with low lectin pathway activity reconstituted with purified human MBL, fully recovered this activity. No deficiencies were found in classical or alternative pathway, whereas the lectin pathway showed reduced activity in a substantial number of pigs, similar to the situation in humans. Finally, the assay was successfully used to evaluate and monitor inhibition of pig complement in vitro and in vivo.

CONCLUSIONS

The human complement Wielisa test can be used for functional evaluation of all complement pathways in pig serum.

Albumin lavage does not improve the outcome of meconium aspiration syndrome

OBJECTIVE

Meconium aspiration syndrome is still a serious condition with high mortality and morbidity. No specific treatment is yet available, although surfactant is known to reduce the need for extracorporeal membrane oxygenation and surfactant lavage has shown promising results in animal studies. Our group has previously shown reduced oxygenation index in an experimental model of meconium aspiration syndrome in newborn pigs when mixing albumin with meconium before endotracheal instillation. Lung compliance increased when albumin was instilled after meconium as a rescue. The aim of this study was to combine the effect of albumin and lavage.

METHODS

Sixteen newborn pigs (six in the meconium-albumin group, six in the meconium group, and four control animals) were anesthetized and tracheotomized. Meconium 4 mL/kg was instilled endotracheally. After five minutes, albumin 15 mL/kg was instilled in the meconium-albumin group followed by endotracheal suctioning. The observation time was six hours. Respiratory and hemodynamic parameters were measured. The terminal complement complex and proinflammatory cytokines were analyzed in plasma.

RESULTS

Oxygenation index, ventilatory index, and the terminal complement complex (sC5b-9) increased significantly in both groups, but significantly more in the meconium-albumin group. Compliance decreased, but significantly more in the meconium-albumin group. The terminal sC5b-9 complex increased in both groups, but significantly more in the meconium-albumin group. Tumor necrosis factor-alpha, interleukin (IL)- 1beta, and IL-6 increased significantly in both groups.

CONCLUSION

Albumin-lavage did not improve the outcome of experimental meconium aspiration syndrome.

The role of complement in meconium aspiration syndrome

The complement system is part of the host defense with a number of biological effects, most of which contribute to the inflammatory reaction by activation of cells like leukocytes and endothelial cells. An intact complement system is required for protection against infection and for maintaining internal inflammatory homeostasis. However, the system is a double-edged sword as improperly or uncontrolled activation is disadvantageous and potentially harmful for the host. Meconium aspiration syndrome (MAS) is associated with a local inflammatory reaction in the lungs, frequently described as a chemical pneumonitis. Cytokines, arachidonic acid metabolites and reactive oxygen species are involved in this reaction. We have recently documented that meconium is a potent activator of complement in vitro and in an experimental piglet model of MAS, the latter presenting with an inflammatory profile closely resembling systemic inflammatory response syndrome. We postulate that complement activation may contribute to the pathogenesis of MAS.

Phospholipase A2 in meconium-induced lung injury

Although the triggering mechanisms of tissue inflammation and injury in meconium-contaminated lungs are still unclear, there is increasing evidence to suggest a central role for phospholipase A(2)'s (PLA(2)). In fact, elevated PLA(2) activities together with high enzyme concentrations, especially the amount of pancreatic (group I) secretory PLA(2) (PLA(2)-I), have been detected in human meconium and in meconium-contaminated lungs. Recent data from our laboratory further indicate that human pancreatic PLA(2), introduced in high amounts within aspirated particulate meconium, is a potent inducer of lung tissue inflammatory injury. Our finding of elevated human PLA(2)-I concentrations in plasma during the first hours after intratracheal meconium administration in newborn piglets further suggests that intrapulmonary aspiration of meconium could also have systemic inflammatory and injurious effects. This, however, remains to be studied in further detail.

Serum cytokine and chemokine profiles in neonates with meconium aspiration syndrome

OBJECTIVES

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.

PATIENTS AND METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Meconium increases type 1 angiotensin II receptor expression and alveolar cell death

The pulmonary renin-angiotensin system (RAS) contributes to inflammation and epithelial apoptosis in meconium aspiration. It is unclear if both angiotensin II receptors (ATR) contribute, where they are expressed and if meconium modifies subtype expression. We examined ATR subtypes in 2 wk rabbit pup lungs before and after meconium exposure and with and without captopril pretreatment or type 1 receptor (AT1R) inhibition with losartan, determining expression and cellular localization with immunoblots, RT-PCR and immunohistochemistry, respectively. Responses of cultured rat alveolar type II pneumocytes were also examined. Type 2 ATR were undetected in newborn lung before and after meconium instillation. AT1R were expressed in pulmonary vascular and bronchial smooth muscle and alveolar and bronchial epithelium. Meconium increased total lung AT1R protein approximately 3-fold (p = 0.006), mRNA 29% (p = 0.006) and immunostaining in bronchial and alveolar epithelium and smooth muscle, which were unaffected by captopril and losartan. Meconium also increased AT1R expression >3-fold in cultured type II pneumocytes and caused concentration-dependent cell death inhibited by losartan. Meconium increases AT1R expression in newborn rabbit lung and cultured type II pneumocytes and induces AT1R-mediated cell death. The pulmonary RAS contributes to the pathogenesis of meconium aspiration through increased receptor expression.

Role of complement and CD14 in meconium-induced cytokine formation

OBJECTIVE

Meconium aspiration syndrome has a complex, poorly defined pathophysiology. Meconium is a potent activator of complement in vitro and in vivo; the latter is associated with a systemic inflammatory response. The complement system and Toll-like receptors are 2 important upstream components of the innate immune system that act partly independently in the inflammatory network. The aim of this study was to investigate the relative role of complement and CD14 in meconium-induced cytokine production.

METHODS

Human adult (n = 6) and cord whole blood (n = 6) anticoagulated with lepirudin was collected and distributed into tubes that contained inhibitory antibodies (anti-CD14, anti-C2, anti-factor D, or combinations thereof). The tubes were preincubated for 5 minutes before addition of meconium or buffer and then incubated for 4 hours at 37 degrees C. Complement activation was measured by quantification of the terminal sC5b-9 complement complex by enzyme-linked immunosorbent assay. A panel of 27 inflammatory mediators (cytokines, chemokines, and growth factors) was measured by using multiplex technology.

RESULTS

Fourteen of the 27 mediators measured were induced by meconium both in cord and adult blood. In cord blood, 2 additional chemokines were induced and the inflammatory response was, in general, more potent. Blocking of complement or CD14 differentially reduced the formation of most mediators, anti-CD14 being more effective. Notably, the combined inhibition of complement and CD14 almost completely abolished meconium-induced formation of the cytokines and the chemokines and markedly reduced the formation of growth factors. The endogenous lipopolysaccharide content of meconium could not explain the CD14-mediated response.

CONCLUSIONS

Meconium-induced triggering of the cytokine network is differentially mediated by complement and CD14. A combined inhibition of these effector mechanisms may be an alternative approach to reduce the inflammatory reaction in meconium aspiration syndrome.

Dysfunction of innate immunity and associated pathology in neonates

The neutrophils and complement system are the critical elements of innate immunity mainly due to participation in the first line of defense against microorganisms by means of phagocytosis, lysis of bacteria and activation of naive B-lymphocytes. In this report we provide an overview of the up to date information regarding the neutrophil and complement system's functional ability in newborn infants in association with the maternal conditions that exist during the intrauterine stage, gestational age and post-neonatal pathology. The neonates' capacity to control the neutrophil and complement protein activation process has also been discussed because of the evidence that uncontrolled activation of these immune elements provides a significant contribution to the tissue damage and subsequent pathology. The authors are confident that despite the many unanswered questions this review updates their knowledge and points the need for further research to clarify the role of the age-associated dysfunction of neutrophils and complement system in the infection and inflammation related pathology of newborn infants.

Meconium Aspiration Syndrome Induces Complement-Associated Systemic Inflammatory Response in Newborn Piglets

The pathophysiology of meconium aspiration syndrome (MAS) is complex. We recently showed that meconium is a potent activator of complement. In the present study, we investigated whether the complement activation occurring in experimental MAS is associated with a systemic inflammatory response as judged by granulocyte activation and cytokine and chemokine release. MAS was induced by the instillation of meconium into the lungs of newborn piglets (n = 8). Control animals (n = 5) received saline under otherwise identical conditions. Haemodynamic and lung dynamic data were recorded. Complement activation, revealed by the terminal sC5b-9 complex (TCC), and cytokines [interleukin (IL)-6 and IL-8] were measured in plasma samples by enzyme immunoassays. The expression of CD18, CD11b and oxidative burst in granulocytes was measured in whole blood by flow cytometry. Plasma TCC increased rapidly in the MAS animals in contrast with controls (P < 0.0005). The TCC concentration correlated closely with oxygenation index (r = 0.48, P < 0.0005) and ventilation index (r = 0.57, P < 0.0005) and inversely with lung compliance (r = -0.63, P < 0.0005). IL-6 and IL-8 increased in MAS animals compared with the controls (P = 0.002 and P < 0.001, respectively). Granulocyte oxidative burst declined significantly in the MAS animals compared with the controls (P < 0.02). TCC correlated significantly with IL-6 (r = 0.64, P < 0.0005) and IL-8 (r = 0.32; P = 0.03) and inversely with oxidative burst (r = -0.37; P = 0.02). A systemic inflammatory response associated with complement activation is seen in experimental MAS. This reaction may contribute to the pathogenesis of MAS.

The diseases treated with ECMO: focus on PPHN

Neonatal extracorporeal support is most often required for neonatal hypoxemic respiratory failure, usually accompanied by persistent pulmonary hypertension of the newborn (PPHN). PPHN is a clinical syndrome that results from the failure of pulmonary vascular transition to extrauterine life. Infants typically present shortly after birth with respiratory distress and cyanosis, but a structurally normal heart. The incidence of PPHN is estimated at 0.2% of live-born term infants. Respiratory failure and hypoxemia in the term newborn result from a heterogeneous group of disorders, and the therapeutic approach and response often depend on the underlying disease. PPHN can largely be thought of as one of three types: (1) the abnormally constricted pulmonary vasculature which is the most common type and includes diagnoses such as meconium aspiration syndrome, respiratory distress syndrome, and sepsis; (2) the structurally abnormal vasculature, which is often termed idiopathic PPHN; or (3) the hypoplastic vasculature such as is seen in congenital diaphragmatic hernia, or alveolar capillary dysplasia, a rare malformation of lung development. The pathophysiology of each type is dependent on the point in gestation when the normal transition to extrauterine life fails. This article will discuss the known pathophysiology in PPHN and new treatment modalities.