Ventilation-mediated injury after preterm delivery of Ureaplasma parvum colonized fetal lambs

Postnatal budesonide improved lung function in preterm lambs exposed to antenatal steroids and chorioamnionitis

BACKGROUND

A combination of budesonide and surfactant decreases the rates of BPD in infants and lung injury in preterm sheep. Whether this combination will show benefit in the setting of chorioamnionitis and antenatal steroids is not known.

METHODS

Ewes at 123 ± 1 day gestational age received intra-amniotic (IA) injections of 10 mg LPS before being randomized to receive either 0.25 mg/kg maternal betamethasone phosphate and acetate or saline by intramuscular (IM) injection at 48 and 24 h prior to delivery at 125 ± 1 day. Lambs (N = 6-9/group) underwent intentionally injurious ventilation for 15 min, then lambs received surfactant mixed with either: (1) saline; or (2) Budesonide 0.25 mg/kg and were ventilated for 4 h.

RESULTS

Compared with LPS-exposed animals that received no IM steroid treatment, betamethasone exposed fetuses had improved hemodynamic stability, lung compliance, and ventilation efficiency. The addition of budesonide to surfactant further improved markers of injury and pro-inflammatory cytokine mRNA in both betamethasone IM or no IM lambs exposed to LPS IA. Antenatal betamethasone and IA LPS exposures decreased budesonide levels in the fetal lung and plasma.

CONCLUSION

Antenatal betamethasone stabilizes physiologic parameters in LPS treated lambs. Budesonide mixed with surfactant further decreases injury and improves respiratory physiology in betamethasone treated animals.

IMPACT

Antenatal betamethasone improved lung and systemic physiology in the setting of intra-amniotic LPS. The addition of budesonide to the surfactant further improved lung function. Budesonide levels in the plasma and lung were lower in lambs exposed to either LPS or LPS and Betamethasone animals, and these findings were not explained by increased esterification in the lungs. The combination of antenatal steroids and budesonide with surfactant had the lowest markers of pro-inflammatory cytokines in the lung of LPS exposed animals.

Preterm ovine respiratory epithelial cell responses to mechanical ventilation, lipopolysaccharide, and interleukin-13

Mechanical ventilation causes airway injury, respiratory epithelial cell proliferation, and lung inflammation in preterm sheep. Whether preterm epithelial cells respond similarly to adult epithelial cells or are altered by mechanical ventilation is unknown. We test the hypothesis that mechanical ventilation alters the responses of preterm airway epithelium to stimulation in culture. Respiratory epithelial cells from the trachea, left mainstem bronchi (LMSB), and distal bronchioles were harvested from unventilated preterm lambs, ventilated preterm lambs, and adult ewes. Epithelial cells were grown in culture or on air-liquid interface (ALI) and challenged with combinations of either media only, lipopolysaccharide (LPS; 10 ng/mL), bronchoalveolar fluid (BALF), or interleukin-13 (IL-13). Cell lysates were evaluated for mRNA changes in cytokine, cell type markers, Notch pathway, and acute phase markers. Mechanical ventilation altered preterm respiratory epithelium cell types. Preterm respiratory epithelial cells responded to LPS in culture with larger IL-8 induction than adults, and mechanical ventilation further increased cytokines IL-1β and IL-8 mRNA induction at 2 h. IL-8 protein is detected in cell media after LPS stimulation. The addition of BALF from ventilated preterm animals increased IL-1β mRNA to LPS (fivefold) in both preterm and adult cells and suppressed IL-8 mRNA (twofold) in adults. Preterm respiratory epithelial cells, when grown on ALI, responded to IL-13 with an increase in goblet cell mRNA. Preterm respiratory epithelial cells responded to LPS and IL-13 with responses similar to adults. Mechanical ventilation or exposure to BALF from mechanically ventilated animals alters the responses to LPS.NEW & NOTEWORTHY Preterm lamb respiratory epithelial cells can be extracted from the trachea and bronchi and frozen, and the preterm cells can respond in culture to stimulation with LPS or IL-13. Brief mechanical ventilation changes the distribution and cell type of preterm respiratory cells toward an adult phenotype, and mechanical ventilation alters the response to LPS in culture. Bronchoalveolar lavage fluid from preterm lambs receiving mechanical ventilation also alters unventilated preterm and adult responses to LPS.

LISA/MIST: Complex clinical problems almost never have easy solutions

Over the last 10 years, new techniques to administer surfactant have been promoted, based on their presumed lesser invasiveness and they have been generally called LISA (less invasive surfactant administration). We believe that the clinical potential of LISA techniques is currently overestimated. LISA lacks biological and pathophysiological background justifying its potential benefits. Moreover, LISA has been investigated in clinical trials without previous translational data and these trials are affected by significant flaws. The available data from these trials only allow to conclude that LISA is better than prolonged, unrestricted invasive ventilation with loosely described parameters, a mode of respiratory support that should be anyway avoided in preterm infants. We urge the conduction of high-quality studies to understand how to choose and titrate analgesia/sedation and optimize surfactant administration in preterm neonates. We offer a comprehensive, evidence-based review of the clinical data on LISA, their biases and the lack of physiopathology background.

Tidal volume measurements in the delivery room in preterm infants requiring positive pressure ventilation via endotracheal tube-feasibility study

OBJECTIVE

Current delivery room (DR) resuscitation utilizes pressure-limited devices without tidal volume (TV) measurements. Clinicians use chest expansion as a surrogate, which is a poor indicator of TV. TV in early life can be highly variable due to rapidly changing lung compliance. Our objectives were to assess feasibility of measuring TV in DR, and to report the generated TV in intubated patients.

STUDY DESIGN

Prospective, observational, feasibility study in infants <32 weeks GA and intubated in DR. TV was measured using a respiratory function monitor.

RESULT

Ten infants with mean GA 23.9(±1.5) weeks and mean BW 618.5(±155) gram were included. Total of 178 min (mean 17.8 min/patient) with 8175 individual breaths (mean 817.5 breaths/patient) were analyzed. Goal TV of 4-6 ml/kg was provided 23.5% of times with high TV (>6 ml/kg) provided 47.7% of times.

CONCLUSION

TV measurement in DR is feasible. It is associated with high intra and inter-patient variability.

Bronchopulmonary dysplasia: Pathophysiology and potential anti-inflammatory therapies

Inflammation of the preterm lungs is key to the pathogenesis of bronchopulmonary dysplasia (BPD), whether it arises as a consequence of intrauterine inflammation or postnatal respiratory management. This review explores steroidal and non-steroidal therapies for reducing neonatal pulmonary inflammation, aimed at treating or preventing BPD.

Impact of delivered tidal volume on the occurrence of intraventricular haemorrhage in preterm infants during positive pressure ventilation in the delivery room

BACKGROUND AND OBJECTIVES

Delivery of inadvertent high tidal volume (V_T) during positive pressure ventilation (PPV) in the delivery room is common. High V_T delivery during PPV has been associated with haemodynamic brain injury in animal models. We examined if V_T delivery during PPV at birth is associated with brain injury in preterm infants <29 weeks' gestation.

METHODS

A flow-sensor was placed between the mask and the ventilation device. V_T values were compared with recently described reference ranges for V_T in spontaneously breathing preterm infants at birth. Infants were divided into two groups: V_T<6  mL/kg or V_T>6 mL/kg (normal and high V_T, respectively). Brain injury (eg, intraventricular haemorrhage (IVH)) was assessed using routine ultrasound imaging within the first days after birth.

RESULTS

A total of 165 preterm infants were included, 124 (75%) had high V_T and 41 (25%) normal V_T. The mean (SD) gestational age and birth weight in high and normal V_T group was similar, 26 (2) and 26 (1) weeks, 858 (251) g and 915 (250) g, respectively. IVH in the high V_T group was diagnosed in 63 (51%) infants compared with 5 (13%) infants in the normal V_T group (P=0.008).Severe IVH (grade III or IV) developed in 33/124 (27%) infants in the high V_T group and 2/41 (6%) in the normal V_T group (P=0.01).

CONCLUSIONS

High V_T delivery during mask PPV at birth was associated with brain injury. Strategies to limit V_T delivery during mask PPV should be used to prevent high V_T delivery.

Dose-dependent exacerbation of ventilation-induced lung injury by erythropoietin in preterm newborn lambs

Erythropoietin (EPO) is being trialled in preterm infants to reduce brain injury, but high doses increase lung injury in ventilated preterm lambs. We aimed to determine whether early administration of lower doses of EPO could reduce ventilation-induced lung injury and systemic inflammation in preterm lambs. Ventilation was initiated in anaesthetized preterm lambs [125 ± 1 (SD) days gestation] using an injurious strategy for the first 15 min. Lambs were subsequently ventilated with a protective strategy for a total of 2 h. Lambs were randomized to receive either intravenous saline (Vent; n = 7) or intravenous 300 ( n = 5), 1,000 (EPO1000; n = 5), or 3,000 (EPO3000; n = 5) IU/kg of human recombinant EPO via an umbilical vein. Lung tissue was collected for molecular and histological assessment of inflammation and injury and compared with unventilated control lambs (UVC; n = 8). All ventilated groups had similar blood gas and ventilation parameters, but EPO1000 lambs had a lower fraction of inspired oxygen requirement and lower alveolar–arterial difference in oxygen. Vent and EPO lambs had increased lung interleukin (IL)-1β, IL-6, and IL-8 mRNA, early lung injury genes connective tissue growth factor, early growth response protein 1, and cysteine-rich 61, and liver serum amyloid A3 mRNA compared with UVCs; no difference was observed between Vent and EPO groups. Histological lung injury was increased in Vent and EPO groups compared with UVCs, but EPO3000 lambs had increased lung injury scores compared with VENT only. Early low-doses of EPO do not exacerbate ventilation-induced lung inflammation and injury and do not provide any short-term respiratory benefit. High doses (≥3,000 IU/kg) likely exacerbate lung inflammation and injury in ventilated preterm lambs.

NEW & NOTEWORTHY Trials are ongoing to assess the efficacy of erythropoietin (EPO) to provide neuroprotection for preterm infants. However, high doses of EPO increase ventilation-induced lung injury (VILI) in preterm lambs. We investigated whether early lower doses of EPO may reduce VILI. We found that lower doses did not reduce, but did not increase, VILI, while high doses (≥3,000 IU/kg) increase VILI. Therefore, lower doses of EPO should be used in preterm infants, particularly those receiving respiratory support.

Ventilation-induced lung injury is not exacerbated by growth restriction in preterm lambs

Intrauterine growth restriction (IUGR) and preterm birth are frequent comorbidities and, combined, increase the risk of adverse respiratory outcomes compared with that in appropriately grown (AG) infants. Potential underlying reasons for this increased respiratory morbidity in IUGR infants compared with AG infants include altered fetal lung development, fetal lung inflammation, increased respiratory requirements, and/or increased ventilation-induced lung injury. IUGR was surgically induced in preterm fetal sheep (0.7 gestation) by ligation of a single umbilical artery. Four weeks later, preterm lambs were euthanized at delivery or delivered and ventilated for 2 h before euthanasia. Ventilator requirements, lung inflammation, early markers of lung injury, and morphological changes in lung parenchymal and vascular structure and surfactant composition were analyzed. IUGR preterm lambs weighed 30% less than AG preterm lambs, with increased brain-to-body weight ratio, indicating brain sparing. IUGR did not induce lung inflammation or injury or alter lung parenchymal and vascular structure compared with AG fetuses. IUGR and AG lambs had similar oxygenation and respiratory requirements after birth and had significant, but similar, increases in proinflammatory cytokine expression, lung injury markers, gene expression, and surfactant phosphatidylcholine species compared with unventilated controls. IUGR does not induce pulmonary structural changes in our model. Furthermore, IUGR and AG preterm lambs have similar ventilator requirements in the immediate postnatal period. This study suggests that increased morbidity and mortality in IUGR infants is not due to altered lung tissue or vascular structure, or to an altered response to early ventilation.

Protective ventilation of preterm lambs exposed to acute chorioamnionitis does not reduce ventilation-induced lung or brain injury

Background

The onset of mechanical ventilation is a critical time for the initiation of cerebral white matter (WM) injury in preterm neonates, particularly if they are inadvertently exposed to high tidal volumes (V_T) in the delivery room. Protective ventilation strategies at birth reduce ventilation-induced lung and brain inflammation and injury, however its efficacy in a compromised newborn is not known. Chorioamnionitis is a common antecedent of preterm birth, and increases the risk and severity of WM injury. We investigated the effects of high V_T ventilation, after chorioamnionitis, on preterm lung and WM inflammation and injury, and whether a protective ventilation strategy could mitigate the response.

Methods

Pregnant ewes (n = 18) received intra-amniotic lipopolysaccharide (LPS) 2 days before delivery, instrumentation and ventilation at 127±1 days gestation. Lambs were either immediately euthanased and used as unventilated controls (LPS_UVC; n = 6), or were ventilated using an injurious high V_T strategy (LPS_INJ; n = 5) or a protective ventilation strategy (LPS_PROT; n = 7) for a total of 90 min. Mean arterial pressure, heart rate and cerebral haemodynamics and oxygenation were measured continuously. Lungs and brains underwent molecular and histological assessment of inflammation and injury.

Results

LPS_INJ lambs had poorer oxygenation than LPS_PROT lambs. Ventilation requirements and cardiopulmonary and systemic haemodynamics were not different between ventilation strategies. Compared to unventilated lambs, LPS_INJ and LPS_PROT lambs had increases in pro-inflammatory cytokine expression within the lungs and brain, and increased astrogliosis (p<0.02) and cell death (p<0.05) in the WM, which were equivalent in magnitude between groups.

Conclusions

Ventilation after acute chorioamnionitis, irrespective of strategy used, increases haemodynamic instability and lung and cerebral inflammation and injury. Mechanical ventilation is a potential contributor to WM injury in infants exposed to chorioamnionitis.

Ventilation-induced increases in EGFR ligand mRNA are not altered by intra-amniotic LPS or ureaplasma in preterm lambs

Chorioamnionitis and mechanical ventilation are associated with bronchopulmonary dysplasia (BPD) in preterm infants. Mechanical ventilation at birth activates both inflammatory and acute phase responses. These responses can be partially modulated by previous exposure to intra-amniotic (IA) LPS or Ureaplasma parvum (UP). Epidermal growth factor receptor (EGFR) ligands participate in lung development, and angiotensin converting enzyme (ACE) 1 and ACE2 contribute to lung inflammation. We asked whether brief mechanical ventilation at birth altered EGFR and ACE pathways and if antenatal exposure to IA LPS or UP could modulate these effects. Ewes were exposed to IA injections of UP, LPS or saline multiple days prior to preterm delivery at 85% gestation. Lambs were either immediately euthanized or mechanically ventilated for 2 to 3 hr. IA UP and LPS cause modest changes in the EGFR ligands amphiregulin (AREG), epiregulin (EREG), heparin binding epidermal growth factor (HB-EGF), and betacellulin (BTC) mRNA expression. Mechanical ventilation greatly increased mRNA expression of AREG, EREG, and HB-EGF, with no additional increases resulting from IA LPS or UP. With ventilation AREG and EREG mRNA localized to cells in terminal airspace. EGFR mRNA also increased with mechanical ventilation. IA UP and LPS decreased ACE1 mRNA and increased ACE2 mRNA, resulting in a 4 fold change in the ACE1/ACE2 ratio. Mechanical ventilation with large tidal volumes increased both ACE1 and ACE2 expression. The alterations seen in ACE with IA exposures and EGFR pathways with mechanical ventilation may contribute to the development of BPD in preterm infants.

Prophylactic erythropoietin exacerbates ventilation-induced lung inflammation and injury in preterm lambs

Ventilation-induced lung injury (VILI) of preterm neonates probably contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). Erythropoietin (EPO) has been suggested as a therapy for BPD. The aim of this study was to determine whether prophylactic administration of EPO reduces VILI in preterm newborn lambs. Lambs at 126 days of gestation (term is 147 days) were delivered and ventilated with a high tidal volume strategy for 15 min to cause lung injury, then received gentle ventilation until 2 h of age. Lambs were randomized to receive intravenous EPO (5000 IU kg(-1): Vent+EPO; n = 6) or phosphate-buffered saline (Vent; n = 7) soon after birth: unventilated controls (UVC; n = 8) did not receive ventilation or any treatment. Physiological parameters were recorded throughout the experimental procedure. Samples of lung were collected for histological and molecular assessment of inflammation and injury. Samples of liver were collected to assess the systemic acute phase response. Vent+EPO lambs received higher F IO 2, P aO 2 and oxygenation during the first 10 min than Vent lambs. There were no differences in physiological indices beyond this time. Total lung injury score, airway wall thickness, inflammation and haemorrhage were higher in Vent+EPO lambs than in Vent lambs. Lung inflammation and early markers of lung and systemic injury were elevated in ventilated lambs relative to unventilated lambs; EPO administration further increased lung inflammation and markers of lung and systemic injury. Prophylactic EPO exacerbates VILI, which may increase the incidence and severity of long-term respiratory disease. More studies are required before EPO can be used for lung protection in preterm infants.

Sustained inflation at birth did not protect preterm fetal sheep from lung injury

Sustained lung inflations (SI) at birth may recruit functional residual capacity (FRC). Clinically, SI increase oxygenation and decrease need for intubation in preterm infants. We tested whether a SI to recruit FRC would decrease lung injury from subsequent ventilation of fetal, preterm lambs. The preterm fetus (128±1 day gestation) was exteriorized from the uterus, a tracheostomy was performed, and fetal lung fluid was removed. While maintaining placental circulation, fetuses were randomized to one of four 15-min interventions: 1) positive end-expiratory pressure (PEEP) 8 cmH2O (n=4), 2) 20 s SI to 50 cmH2O then PEEP 8 cmH2O (n=10), 3) mechanical ventilation at tidal volume (VT) 7 ml/kg (n=13), or 4) 20 s SI then ventilation at VT 7 ml/kg (n=13). Lambs were ventilated with 95% N2/5% CO2 and PEEP 8 cmH2O. Volume recruitment was measured during SI, and fetal tissues were collected after an additional 30 min on placental support. SI achieved a mean FRC recruitment of 15 ml/kg (range 8-27). Fifty percent of final FRC was achieved by 2 s, 65% by 5 s, and 90% by 15 s, demonstrating prolonged SI times are needed to recruit FRC. SI alone released acute-phase proteins into the fetal lung fluid and increased mRNA expression of proinflammatory cytokines and acute-phase response genes in the lung. Mechanical ventilation further increased all markers of lung injury. SI before ventilation, regardless of the volume of FRC recruited, did not alter the acute-phase and proinflammatory responses to mechanical ventilation at birth.

Effects of chorioamnionitis on the fetal lung

Very preterm infants are commonly exposed to a chronic, often asymptomatic, chorioamnionitis that is diagnosed by histologic evaluation of the placenta only after delivery. The reported effects of these exposures on fetal lungs are inconsistent because exposure to different organisms, durations of exposure, and fetal/maternal responses affect outcomes. In experimental models, chorioamnionitis can both injure and mature the fetal lung and cause immune nodulation. Postnatal care strategies also change how chorioamnionitis relates to clinical outcomes such as bronchopulmonary dysplasia.

Comparison of poractant alfa and lyophilized lucinactant in a preterm lamb model of acute respiratory distress

INTRODUCTION

A lyophilized formulation of lucinactant has been developed to simplify preparation and dosing. Endotracheal administration of surfactant can be associated with potentially harmful transient hemodynamic changes including decreases in cerebral blood flow and delivery of O2 to the brain. Efficacy and peri-dosing effects of poractant alfa and a lyophilized form of lucinactant were compared in this study.

METHODS

Premature lambs (126-129 d gestation) were delivered by c-section, tracheostomized, ventilated, and instrumented with cerebral laser Doppler flowmetry and tissue PO2 probes. Pulmonary compliance and tidal volumes were monitored continuously and surfactant lung distribution was assessed. Lambs received either poractant alfa or lyophilized lucinactant and were monitored for 3 h after treatment.

RESULTS

Both groups showed significant improvements in arterial pCO2, pH, pulmonary compliance, and tidal volume (all P < 0.01), a similar intra-pulmonary distribution profile, and no significant changes in arterial blood pressure or cerebral blood flow. Administration of poractant alfa was associated with higher mean airway pressures from 75 min post-dosing and transiently decreased heart rate and increased brain tissue PO2 during the first 30 min after treatment.

DISCUSSION

In this newborn lamb model of respiratory distress, lyophilized lucinactant results in improved lung function as compared with poractant alfa.

Initiation of resuscitation with high tidal volumes causes cerebral hemodynamic disturbance, brain inflammation and injury in preterm lambs

AIMS

Preterm infants can be inadvertently exposed to high tidal volumes (V(T)) in the delivery room, causing lung inflammation and injury, but little is known about their effects on the brain. The aim of this study was to compare an initial 15 min of high V(T) resuscitation strategy to a less injurious resuscitation strategy on cerebral haemodynamics, inflammation and injury.

METHODS

Preterm lambs at 126 d gestation were surgically instrumented prior to receiving resuscitation with either: 1) High V(T) targeting 10-12 mL/kg for the first 15 min (n = 6) or 2) a protective resuscitation strategy (Prot V(T)), consisting of prophylactic surfactant, a 20 s sustained inflation and a lower initial V(T) (7 mL/kg; n = 6). Both groups were subsequently ventilated with a V(T) 7 mL/kg. Blood gases, arterial pressures and carotid blood flows were recorded. Cerebral blood volume and oxygenation were assessed using near infrared spectroscopy. The brain was collected for biochemical and histologic assessment of inflammation, injury, vascular extravasation, hemorrhage and oxidative injury. Unventilated controls (UVC; n = 6) were used for comparison.

RESULTS

High V(T) lambs had worse oxygenation and required greater ventilatory support than Prot V(T) lambs. High V(T) resulted in cerebral haemodynamic instability during the initial 15 min, adverse cerebral tissue oxygenation index and cerebral vasoparalysis. While both resuscitation strategies increased lung and brain inflammation and oxidative stress, High V(T) resuscitation significantly amplified the effect (p = 0.014 and p<0.001). Vascular extravasation was evident in the brains of 60% of High V(T) lambs, but not in UVC or Prot V(T) lambs.

CONCLUSION

High V(T) resulted in greater cerebral haemodynamic instability, increased brain inflammation, oxidative stress and vascular extravasation than a Prot V(T) strategy. The initiation of resuscitation targeting Prot V(T) may reduce the severity of brain injury in preterm neonates.

Transplacental transfer of medetomidine and ketamine in pregnant ewes

The extent of placental transfer of medetomidine and ketamine is unknown in pregnant ewes. Date-mated singleton (n = 8) and twin (n = 8) pregnant merino cross ewes were anaesthetized for Caesarean delivery of preterm lamb fetuses. A combination of medetomidine (20 μg/kg) and ketamine (10 mg/kg) was administered by intravenous injection and surgery performed immediately thereafter. Blood samples were collected from the ewe at one, five and 10 min after intravenous injection and from the umbilical vein of the fetus at delivery. Non-pregnant ewes were also anaesthetized (n = 8). There was no difference in the plasma concentration of medetomidine or ketamine when comparing singleton and twin ewes or pregnant and non-pregnant ewes for the short duration of the study. Fetal plasma concentrations of each drug were comparable to the maternal concentrations at the same time. We conclude that both drugs cross the placenta readily and provide anaesthesia and analgesia for the fetus when it is delivered.

Targeting inflammation to prevent bronchopulmonary dysplasia: can new insights be translated into therapies?

Bronchopulmonary dysplasia (BPD) frequently complicates preterm birth and leads to significant long-term morbidity. Unfortunately, few therapies are known to effectively prevent or treat BPD. Ongoing research has been focusing on potential therapies to limit inflammation in the preterm lung. In this review we highlight recent bench and clinical research aimed at understanding the role of inflammation in the pathogenesis of BPD. We also critically assess currently used therapies and promising developments in the field.

Chorioamnionitis - new ideas from experimental models

Antenatal inflammation may be associated with adverse neonatal outcomes in several organ systems. Bacteria and a few viruses have been detected in cases of microbial invasion of the amniotic cavity which is referred to as chorioamnionitis. Many aspects of this disease remain unclear such as the causes, time of onset and the fetal responses. Chorioamnionitis was therefore induced in pregnant sheep by injections of lipopolysaccharide (LPS) or Ureaplasma species into the amniotic cavity under ultrasound guidance. LPS-induced chorioamnionitis caused a cascade of organ injury, inflammation, and remodeling. The organ-specific changes were accompanied by systemic effects. The systemic effects after LPS-induced chorioamnionitis resulted in immune suppression against several Toll-like receptor agonists (cross-tolerance). Ureaplasma induced chorioamnionitis made changes in the fetal lung structure depending on the time of infection during pregnancy. The mechanisms of inflammation, structural damage and decreased expression of growth factors need to be further studied to determine therapeutic targets in suitable animal models.

Inflammation in fetal sheep from intra-amniotic injection of Ureaplasma parvum

Bronchopulmonary dysplasia is associated with chorioamnionitis and fetal lung inflammation. Ureaplasma species are the bacteria most frequently isolated from chorioamnionitis. Very chronic ureaplasma colonization of amniotic fluid causes low-grade lung inflammation and functional lung maturation in fetal sheep. Less is known about shorter exposures of the fetal lung. Therefore, we hypothesized that ureaplasmas would cause an acute inflammatory response that would alter lung development. Singleton ovine fetuses received intra-amniotic Ureaplasma parvum serovar 3 or control media at 110, 117, or 121 days and were delivered at 124 days gestational age (term = 150 days). Inflammation was assessed by 1) cell counts in bronchoalveolar lavage fluid (BALF), and 2) cytokine mRNA measurements, immunohistochemistry, and flow cytometry for inflammatory cells and elastin and α-smooth muscle actin (α-SMA) staining in lung tissue. Neutrophils were increased in BALF 3 days after exposure to ureaplasmas (P = 0.01). Myeloperoxidase-positive cells increased after 3 days (P = 0.03), and major histocompatibility complex (MHC) class II-positive cells increased after 14 days of ureaplasma exposure (P = 0.001). PU.1 (macrophage marker)- or CD3 (T lymphocyte marker)-positive cells were not induced by ureaplasmas. CD3-positive cells in the posterior mediastinal lymph node increased in ureaplasma-exposed animals at 3, 7, and 14 days (P = 0.002). Focal elastin depositions decreased in alveolar septa at 14 days (P = 0.002), whereas α-SMA increased in arteries and bronchioli. U. parvum induced a mild acute inflammatory response and changed elastin and α-SMA deposition in the lung, which may affect lung structure and subsequent development.