Angiotensin II receptor blockade inhibits pneumocyte apoptosis in experimental meconium aspiration

Time-Dependent Oxidative Alterations in Plasma and Lung Tissue after Meconium Aspiration in a Rabbit Model

Aspirated meconium into a newborn's airways induces the transcription of pro-oxidative mediators that cooperate in the pathogenesis of inflammatory changes and may negatively affect the commonly used exogenous surfactant therapy. However, inflammation is not treated at present, nor is the time dependence of oxidative damage known. The aim of our study was to describe the time course of oxidative stress marker production during meconium aspiration syndrome (MAS) and its relationship to leukocyte infiltration. New Zealand rabbits were instilled with saline or meconium suspension and ventilated for 5.5 h. Respiratory parameters were recorded and blood samples were taken before meconium application and in time intervals of 15 and 30 min, 1.0, 1.5, 3.5 and 5.5 h after application to evaluate oxidative markers and differential leukocytes count. Meconium aspiration led to a worsening of respiratory parameters and a decrease in leukocytes in the first 15 min. Changes in leukocytes were correlated both with nitrotyrosine (3NT) levels and thiobarbituric acid reactive substance (TBARS) levels, with the latter also related to changes in neutrophil count. The production of 3NT and TBARS increased in 1.5 and 3.5 h, respectively, in different ways, suggesting more than one source of oxidative agents and a potential risk of exogenous surfactant inactivation in a short time. We observed that MAS triggered neutrophil migration to the alveolar space and activation, as shown by the increased expression of pro-inflammatory cytokines and generation of indicators of oxidative damage to proteins and lipids during the time period when iNOS and NO metabolites were released.

ACE2-like enzyme B38-CAP suppresses abdominal sepsis and severe acute lung injury

Angiotensin-converting enzyme 2 (ACE2) is the carboxypeptidase to degrade angiotensin II (Ang II) to angiotensin 1–7 (Ang 1–7) and improves the pathologies of cardiovascular disease and acute respiratory distress syndrome (ARDS)/acute lung injury. B38-CAP is a bacteria-derived ACE2-like carboxypeptidase as potent as human ACE2 and ameliorates hypertension, heart failure and SARS-CoV-2-induced lung injury in mice. Recombinant B38-CAP is prepared with E. coli protein expression system more efficiently than recombinant soluble human ACE2. Here we show therapeutic effects of B38-CAP on abdominal sepsis- or acid aspiration-induced acute lung injury. ACE2 expression was downregulated in the lungs of mice with cecal ligation puncture (CLP)-induced sepsis or acid-induced lung injury thereby leading to upregulation of Ang II levels. Intraperitoneal injection of B38-CAP significantly decreased Ang II levels while upregulated angiotensin 1–7 levels. B38-CAP improved survival rate of the mice under sepsis. B38-CAP suppressed the pathologies of lung inflammation, improved lung dysfunction and downregulated elevated cytokine mRNA levels in the mice with acute lung injury. Thus, systemic treatment with an ACE2-like enzyme might be a potential therapeutic strategy for the patients with severe sepsis or ARDS.

Effects of intratracheal captopril on severely meconium-injured piglet lungs

BACKGROUND

Severe meconium aspiration syndrome (MAS) may cause intractable respiratory failure in neonates. Targeting the renin-angiotensin system may be an effective way to treat such pulmonary dysfunction. Captopril has the potential to mitigate the severity of lung injury by inhibiting angiotensin-converting enzyme.

METHODS

Twelve newborn piglets were intratracheally instilled with human meconium to induce severe MAS and were randomly treated with IT administration of captopril (0.5 mg/kg) (IT-Cap group, n = 6), or sham air instillation (Control group, n = 6). Cardiopulmonary profiles were monitored for a total of 5 hours. Pulmonary history was examined to compare lung injury severity between groups.

RESULTS

There were no significant differences between the two study groups in gas exchange and lung compliance, peak inspiratory pressure, heart rate, and mean arterial blood pressure over the 5-h experimental period, but there were trends toward lower blood pressure and pH in the IT-Cap group. Histopathological examinations revealed significantly higher lung injury scores in the dependent site of the control group than in the nondependent site of the control group and both sites of the IT-Cap group.

CONCLUSION

Intratracheal captopril did not present significant beneficial effects on severe meconium-injured lungs within 5 hours after injury. Further studies with different disease severities and dosing strategies are required.

Erythropoietin may attenuate lung inflammation in a rat model of meconium aspiration syndrome

BACKGROUND

Inflammation is believed to play a key role in the pathophysiology of meconium aspiration syndrome (MAS).

PURPOSE OF THE STUDY

The objective was to determine whether the recombinant human Erythropoietin (rhEPO) pretreatment could attenuate meconium-induced inflammation.

MATERIALS AND METHODS

In this study, 24 ventilated adult male rats were studied to examine the effects of recombinant human EPO (rhEPO) on meconium-induced inflammation. Seventeen rats were instilled with human meconium (1.5 mL/kg, 65 mg/mL) intratracheally and ventilated for 3 hours. rhEPO (1000 U/kg) (n = 9) or saline (n = 8) was given to the animals. Seven rats that were ventilated and not instilled with meconium served as a sham-controlled group. Analysis of the blood gases, interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α in blood and bronchoalveolar lavage (BAL) fluid samples, and lung tissue myeloperoxidase levels were performed.

RESULTS

Intrapulmonary instillation of meconium resulted in the increase of TNF-α (p = 0.005 and p < 0.001, respectively) and IL-8 concentrations (p < 0.001 and p < 0.001, respectively) in BAL fluid in the EPO + meconium and saline + meconium groups compared with the sham-controlled group. rhEPO pretreatment prevented the increase of BAL fluid IL-1β, IL-6, and IL-8 levels (p < 0.001, p = 0.021, and p = 0.005, respectively), and serum IL-6 levels (p = 0.036).

CONCLUSION

rhEPO pretreatment is associated with improved BAL fluid and serum cytokine levels. Pretreatment with rhEPO might reduce the risk of developing of meconium-induced derangements.

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.

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.

Meconium exposure dependent cell death and apoptosis in human alveolar epithelial cells

Alveolar epithelial cells of neonates are directly exposed to aspirated meconium during meconium aspiration syndrome (MAS). This study was designed to investigate the influence of quantity and time of meconium exposure on the cell viability and caspase activity in type II human alveolar epithelial cells. Human alveolar epithelial cells were incubated with human meconium suspension at different concentrations and for different times. Cell viability and DNA fragmentation were investigated together with caspases activity and the amount of Bcl-2 protein present. We found that cell viability was significantly lower in cells exposed to a higher concentration of meconium. This was also true for cells exposed to meconium for longer. Significantly higher DNA fragmentation, an approximately two- to fivefold increase, was observed in cells that had been exposed to higher (5% and 10%) concentration of meconium compared to those treated with lower (0.1% and 1%) concentrations (P < 0.05). The activity of most apoptotic initiators (caspase 2, 8, 9, 10) and effectors (caspase 3, 6) were found to be significantly higher in cells subject to greater meconium exposure compared to cells with no or minor meconium exposure. The level of Bcl-2 was also found to be significantly decreased in meconium-exposed cells (P < 0.05). In conclusion, human meconium would seem to induce direct cell death as well as caspase-dependent apoptosis in alveolar epithelial cells; the amount and period of exposure to meconium are crucial factors in this process. Thus, removing aspirated meconium should alleviate lung cell damage in neonates and improve the outcome with MAS.

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.

Meconium aspiration syndrome (MAS) - Where do we go? Research perspectives

The pathogenetic cascade of meconium aspiration syndrome (MAS) in newborn infants is complex and still incompletely studied. The variable clinical presentation of MAS is basically connected with variation of the amount and consistency of aspirated meconium and also its distribution within the affected lungs. The contributing role of other factors, like intrauterine fetal compromises, lung maturity at the time of insult as well as direct and indirect effects of meconium and its components on the lung alveolar and vascular integrity and development, remains to be studied in further detail. Better understanding of the lung injury processes in MAS, specifically inflammatory injury and non-inflammatory apoptosis and their interplay, may offer new possibilities to treat the severely affected infants, and needs therefore to be explored. Systemic dispersion of intrapulmonary meconium and its components may further induce inflammatory circulatory changes and injurious effects in distant organs, but the mechanisms and clinical significance of these systemic complications are still poorly known. It is thus evident that lung injury processes and potent long-term consequences in various extrapulmonary organs, specifically the brain, as well as development of new approaches to their treatment and prevention form great challenges for future research of MAS.

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.

Angiotensin II in apoptotic lung injury: potential role in meconium aspiration syndrome

Meconium aspiration injures a number of cell types in the lung, most notably airway and alveolar epithelial lining cells. Recent data show that at least some of the cell death induced by meconium occurs by apoptosis, and therefore has the potential for pharmacologic inhibition through the use of apoptosis blockers or other strategies. Related work in adult animal models of lung injury has shown that apoptosis of lung epithelial cells induces a local (that is, entirely lung tissue specific) renin-angiotensin system (RAS(L)). Furthermore, this inducible RAS(L) is required for the apoptotic response and affects other adjacent cell types through the release of angiotensin II and related peptides. This manuscript reviews the published data supporting this viewpoint as well as more recent works that suggest the involvement of a RAS(L) in the perinatal lung damage associated with meconium aspiration syndrome (MAS). The implications of these findings regarding their potential for the clinical management of MAS are also discussed.

Inflammatory Response and Apoptosis in Newborn Lungs after Meconium Aspiration

An important feature of meconium-instilled newborn lungs is an inflammatory response and apoptotic cell death. It was recently demonstrated by our group and supported by several other investigators in a relatively short period of time. Apoptosis exists also in healthy lungs, but in meconium-instilled lungs its level is usually dramatically higher. Apoptosis is characterized by loss of cell function, decrease in cell size, and its morphology. Apoptosis plays an important role in normal cell life, but increased levels of apoptosis induce great damage for any tissues. Apoptosis in the lungs has been greatly overlooked for the past decade, and meconium-induced apoptosis is a relatively new event and not effectively studied at the present time. This Review summarized current knowledge regarding meconium-induced inflammation and apoptosis in newborn lungs.

Human meconium has a pulmonary vascular and airway smooth muscle relaxant effect

Meconium aspiration is believed to cause persistent pulmonary hypertension syndrome of the newborn (PPHN) via vasoconstriction, whereas meconium has a relaxant effect on rat tracheal muscle. We evaluated the meconium effect on lung vascular and airway muscle. Three-days old and adult rat 3rd-4th generation arteries and adjacent bronchi were studied in vitro. Fresh homogenized meconium did not induce arterial or airway muscle contraction. In precontracted arteries, meconium induced muscle relaxation that was greater (p < 0.01) in the newborn (53 +/- 5%), when compared with adult vessels (34 +/- 3%). This relaxant response was partially abrogated (p < 0.01) by L-NAME (28 +/- 4%) and enhanced by a superoxide scavenger (55 +/- 4%). Precontracted bronchial muscle relaxed to meconium in vitro and the magnitude of response was greater in the adult when compared with the newborn (p < 0.01). In vitro incubation with meconium (3 h) reduced agonist-stimulated force and enhanced endothelium-dependent relaxation (p < 0.01). Airway meconium instillation followed by mechanical ventilation enhanced thromboxane-induced newborn rat pulmonary arterial muscle contraction in vitro (p < 0.01). We conclude that meconium is a pulmonary vasodilator in vitro Meconium is first noted to be present at 12 wk gestation in humans. It is the by-product of fetal amniotic fluid, lanugo, skin cells, and vernix caseosa swallowing, as well it contains cells derived from the gastrointestinal tract (). Meconium composition also includes four different biliary acids (cholic, chenodeoxycholic, deoxycholic, and lithocholic) and minerals of which copper, zinc, magnesium, calcium iron, and phosphorus are the most common (). In addition, it contains plasmatic proteins such as alpha1-antitripsin and phospholipase A2 (4,5).

Low inflammatory activation by self-assembling Rosette nanotubes in human Calu-3 pulmonary epithelial cells

Rosette nanotubes (RNT) are a new class of metal-free organic nanotubes synthesized through self-assembly. Because of the wide range of potential biomedical applications associated with these materials, it is necessary to evaluate their potential in vitro toxicity. Here the cytotoxicity of a lysine-functionalized nanotube (RNT-K) in a human Calu-3 pulmonary epithelial cell line is investigated. The cells were treated with media only (control), lysine (50 mg mL(-1)), RNT-K (1, 5, and 50 microg mL(-1)), Min-U-Sil quartz microparticles (QM; 80 microg mL(-1)), and lipopolysaccharide (LPS; 1 microg mL(-1)). The supernatants were analyzed at 1, 6, and 24 h after treatment for the expression of three proinflammatory mediators: IL-8, TNF-alpha and EMAP-II. Cellular viability determined with the Trypan blue assay is significantly reduced in the QM and high-dose RNT-treated groups. TNF-alpha and EMAP-II are undetectable by enzyme-linked-immunosorbent assay (ELISA) in the supernatant of all groups. Although IL-8 concentrations do not differ between treatments, its concentrations increase with time within each of the groups. Quantitative reverse-transcriptase polymerase chain reaction (qRTPCR) of IL-8 mRNA shows increased expression in the high-dose RNT-treated groups at both 1 and 6 h, while an adhesion molecule, ICAM-1 mRNA, shows the greatest increase at 6 h in the QM-treated group. In summary, RNT-K neither reduces cell viability at moderate doses nor does it induce a time-dependent inflammatory response in pulmonary epithelial cells in vitro.

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.

Losartan attenuates ventilator-induced lung injury

BACKGROUND

Accumulating evidence shows that angiotensin II (ANG II) can be generated locally in the lung tissue and may have autocrine and/or paracrine actions on the cellular level. In addition, ANG II precursor, angiotensinogen, as well as ANG II type 1 receptor (AT(1)), are also expressed in the lung tissue. Recent studies revealed that ANG II promoted acute lung injury induced by acid aspiration or sepsis, and that ANG II receptor blockade had a protective effect against acute lung injury. Therefore, the authors hypothesized that ventilator-induced lung injury might also be exacerbated by local ANG II action, and that ANG II receptor blockade would protect the lung from ventilator-induced lung injury.

MATERIALS AND METHODS

Forty Sprague Dawley rats weighing 300-350 g were randomly divided into the following experimental groups (10 rats in each group): (1) control group: rats were unventilated; (2) LVT (low volume ventilation) group: rats were ventilated with 8 mL/kg tidal volume room air for 2 h; (3) HVT (high volume ventilation) group: rats were ventilated with 40 mL/kg tidal volume room air for 2 h; (4) HVT + Losartan group: rats were pretreated with Losartan (30 mg/kg, i.p.) prior to high volume ventilation. The samples of pulmonary tissue and lung lavage fluid were collected after experiments. The expression of angiotensinogen and AT(1) receptor mRNA in lung tissue was measured by reverse transcriptase-polymerase chain reaction. Apoptosis of the lung cells was assayed with terminal deoxynucleodityl transferase-mediated nick-end labeling method. Lung pathological changes were examined with optical microscopy. Total protein, wet/dry ratios (W/D), myeloperoxidase (MPO) activity, and neutrophil counts of the lung tissue or lavage fluid were measured with corresponding methods.

RESULTS

Compared with control or LVT, HVT caused significant ventilator-induced lung injury and increased the expression of angiotensinogen and AT(1) receptor mRNA in the lung. Total protein, the number of apoptotic cells, W/D ratio, MPO activity, and neutrophil counts were significantly higher in the HVT group than in the LVT or control group. Pretreatment with Losartan attenuated ventilator-induced lung injury and prevented the increase in total protein, the number of apoptotic cells, W/D ratio, MPO, and neutrophil counts caused by high volume ventilation.

CONCLUSION

Our study indicates that HVT causes remarkable lung injury and up-regulates angiotensinogen and AT(1) receptor expression of in the lung, and that Losartan, a selective inhibitor of subtype AT(1) receptors for angiotensin II, can relieve acute lung injury caused by high volume ventilation.

Lung epithelial cell apoptosis during acute lung injury in infancy

CONTEXT

Apoptosis of lung epithelial cells is implicated in the pathogenesis of acute lung injury. Most research on this subject has focused on adults. Very little is known about a potential interaction of this process with lung development in children.

OBJECTIVE

To summarize the current literature on lung epithelial cell apoptosis and common causes of acute lung injury in infants and young children and to identify new areas of research.

DESIGN

A Medline-based literature search.

RESULTS AND CONCLUSIONS

Few studies have focused on lung epithelial cell apoptosis during common causes of acute lung injury in children. Nevertheless, the limited literature suggests that this may be an important mechanism during respiratory distress syndrome of infants and viral respiratory tract infection. Apoptosis is an essential process during lung development and maturation. Insufficient attention has been paid to potential consequences of this for the short- and long-term outcomes of acute lung injury.

The renin-angiotensin system in acute respiratory distress syndrome

Angiotensin-converting enzyme 2 (ACE2) counterbalances with ACE and functions as a negative regulator of the renin–angiotensin system (RAS). The importance of RAS in acute respiratory distress syndrome (ARDS) has recently re-emerged owing to the identification of ACE2 as a receptor for the SARS-coronavirus. Recent studies have demonstrated that ACE2 protects mice from acute lung injury as well as SARS-mediated lung injury. We review the role of the RAS, in particular ACE2, in the pathogenesis of ARDS.

Terry Delovitch – The John P. Robarts Research Institute, London, Ont., Canada

David Scott – University of Maryland School of Medicine, Baltimore, MD, USA

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.

Inhibition of COX-2 aggravates neutrophil migration and pneumocyte apoptosis in surfactant-depleted rat lungs

Pulmonary inflammation and parenchymal apoptosis are implicated in the pathogenesis of the acute lung injury, but the mechanisms of these reactions are still unclear. Because inhibition of the proinflammatory cyclo-oxygenase (COX)-2 enzyme action is proposed to be useful in various inflammatory lung injuries, we decided to investigate the expression of COX-2 and the possible beneficial effects of its inhibition on pulmonary inflammation and apoptosis in surfactant-depleted lungs. The injury was induced in 2-mo-old rats by repeated lung lavage to remove alveolar surfactant. Eight of these rats were pretreated with a specific COX-2 inhibitor, NS-398. All rats, including control rats without lung lavage, were ventilated with 60% oxygen for 5 h, and the lungs were then studied histologically for tissue injury and with DNA nick-end labeling, cleaved caspase-3 immunohistochemistry, and electron microscopy for apoptotic cell death. Lung tissue myeloperoxidase activity and the expression of COX-2 protein and concentration of prostaglandin E2 were additionally analyzed. Lung lavage increased pulmonary neutrophil migration, histologic injury, and the occurrence of epithelial apoptosis. In contrast, expression of COX-2 and amount of PGE2 were significantly lower in surfactant-depleted lungs than controls. Pretreatment with the COX-2 inhibitor further increased the migration of neutrophils and occurrence of epithelial apoptosis in the surfactant-depleted lungs, compared with nontreated insulted lungs. These results suggest that specific inhibitors of COX-2 should be used cautiously in association with surfactant-deficient lung injuries.

Deletion allele of angiotensin-converting enzyme is associated with increased risk and severity of bronchopulmonary dysplasia

OBJECTIVE

To explore whether the deletion (D) allele of angiotensin-converting enzyme (ACE) is associated with the risk or severity of bronchopulmonary dysplasia (BPD) among very low birth weight (BW) infants.

STUDY DESIGN

Infants with a BW < or = 1250 g were prospectively recruited. The D and I (insertion) alleles of ACE were determined using a polymerase chain reaction followed by restriction fragment length polymorphism analysis.

RESULTS

Infants with DD/DI genotype of ACE had a (mean +/- SD) birth weight (938 +/- 204 g vs 925 +/- 196 g) and gestational age (28 +/- 3 weeks vs 28 +/- 2 weeks), similar to infants with II genotype of ACE (P > .05). Infants with DD/DI genotype of ACE were more likely to have BPD than infants with II genotype (47% vs 22%, P = .025). Among infants with BPD, ACE DD/DI genotype was more common among infants with moderate or severe BPD compared with infants with mild BPD (74% vs 26%, P = .012). The number of D alleles of ACE correlated directly and positively with the severity of BPD (R = 0.23, P = .045).

CONCLUSION

The D allele of ACE is associated with an increased risk and severity of BPD among preterm infants.

Genetic polymorphisms in sepsis

CONTEXT

Wide variability exists in the susceptibility to and outcome from sepsis even within similar intensive care unit populations. Some of this variability in the host may be due to genetic variation in genes coding for components of the innate immune response.

OBJECTIVE

To review the evidence for a genetic influence on the susceptibility to and outcome from sepsis.

DESIGN

Literature review.

PATIENTS

Variety of adult and pediatric patients with various critical illnesses and infections.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Susceptibility to clinical symptoms of sepsis and outcome as measured by severity of disease and mortality.

RESULTS

Polymorphisms in genes coding for proteins involved in the recognition of bacterial pathogens (Toll-like receptor 4, CD14, Fc(gamma)RIIa, and mannose-binding lectin) and the response to bacterial pathogens (tumor necrosis factor-alpha, interleukin (IL)-1alpha, IL-1beta, IL-1 receptor agonist, IL-6, IL-10, heat shock proteins, angiotensin I converting enzyme, plasminogen activator inhibitor-1) can influence the amount or function of the protein produced in response to bacterial stimuli. Evidence is discussed suggesting that some of these genetic polymorphisms influence the susceptibility to and outcome from sepsis.

CONCLUSION

Host genetic variability in the regulatory and coding regions of genes for components of the innate immune system may influence the susceptibility to and/or outcome from sepsis. The disparate results observed in many studies of polymorphisms in sepsis emphasize the need for future studies to be larger, to include the analysis of multiple polymorphisms, and to be better designed with respect to control populations to identify the degree of influence that genetic variability has on sepsis.

Angiotensin II receptor inhibition prevents pneumocyte apoptosis in surfactant-depleted rat lungs

Pneumocyte apoptosis is implicated in the pathophysiology of acute inflammatory lung injuries in newborns and adults. Pulmonary angiotensin (ANG) II contributes to lung epithelial apoptosis in vitro, but its role in acute lung injury in vivo is unclear. We therefore studied the effects of ANG II receptor action on the pulmonary inflammatory and apoptotic changes in surfactant-depleted lungs in rats. Lung injury was induced by repeated lung lavage with saline, and the rats were then ventilated with 60% oxygen for 1, 3, or 5 hr. Separate groups of rats were pretreated with a nonspecific ANG II receptor inhibitor saralasin, the specific ANG II type 1 receptor antagonist losartan, or ANG II type 2 receptor inhibitor PD123319, and were similarly studied. Lungs were studied histologically for tissue injury, and with terminal deoxynucleodityl transferase-mediated dUTP nick end-labeling (TUNEL) and cleaved caspase 3 antibody staining, and by electron microscopy for apoptotic cell death. Surfactant-depleted lungs showed an increased number of TUNEL-positive epithelial cells throughout the study, and intrapulmonary leukocyte migration and histological tissue injury scores were similarly elevated, compared to controls, from 1-5 hr of ventilation. Pretreatment with saralasin or losartan significantly prevented the increase of TUNEL positivity in pneumocytes, but had no effect on the amount of neutrophil influx or total injury score in lavaged lungs. In contrast, administration of PD123319 did not affect the number of TUNEL-positive epithelial cells or histological injury . The results suggest that increased epithelial apoptosis in surfactant-deficient lungs is mediated by ANG II receptor (specifically, subtype 1) action.