Postnatal steroids as lung protective and anti-inflammatory in preterm lambs exposed to antenatal inflammation.

BACKGROUND: Lung inflammation and impaired alveolarization precede bronchopulmonary dysplasia (BPD). Glucocorticoids are anti-inflammatory and reduce ventilator requirements in preterm infants. However, high-dose glucocorticoids inhibit alveolarization. The effect of glucocorticoids on lung function and structure in preterm newborns exposed to antenatal inflammation is unknown. We hypothesise that postnatal low-dose dexamethasone reduces ventilator requirements, prevents inflammation and BPD-like lung pathology, following antenatal inflammation. METHODS: Pregnant ewes received intra-amniotic LPS (E.coli, 4 mg/mL) or saline at 126 days gestation; preterm lambs were delivered 48 h later. Lambs were randomised to receive either tapered intravenous dexamethasone (LPS/Dex, n = 9) or saline (LPS/Sal, n = 10; Sal/Sal, n = 9) commencing <3 h after birth. Respiratory support was gradually de-escalated, using a standardised protocol aimed at weaning from ventilation towards unassisted respiration. Tissues were collected at day 7. RESULTS: Lung morphology and mRNA levels for inflammatory mediators were measured. Respiratory support requirements were not different between groups. Histological analyses revealed higher tissue content and unchanged alveolarization in LPS/Sal compared to other groups. LPS/Dex lambs exhibited decreased markers of pulmonary inflammation compared to LPS/Sal. CONCLUSION: Tapered low-dose dexamethasone reduces the impact of antenatal LPS on ventilation requirements throughout the first week of life and reduces inflammation and pathological thickening of the preterm lung IMPACT: We are the first to investigate the combination of antenatal inflammation and postnatal dexamethasone therapy in a pragmatic study design, akin to contemporary neonatal care. We show that antenatal inflammation with postnatal dexamethasone therapy does not reduce ventilator requirements, but has beneficial maturational impacts on the lungs of preterm lambs at 7 days of life. Appropriate tapered postnatal dexamethasone dosing should be explored for extuabtion of oxygen-dependant neonates.

Intrauterine inflammation exacerbates maladaptive remodeling of the immature myocardium after preterm birth in lambs.

BACKGROUND: Antenatal conditions that are linked with preterm birth, such as intrauterine inflammation, can influence fetal cardiac development thereby rendering the heart more vulnerable to the effects of prematurity. We aimed to investigate the effect of intrauterine inflammation, consequent to lipopolysaccharide exposure, on postnatal cardiac growth and maturation in preterm lambs. METHODS: Preterm lambs (~129 days gestational age) exposed antenatally to lipopolysaccharide or saline were managed according to contemporary neonatal care and studied at postnatal day 7. Age-matched fetal controls were studied at ~136 days gestational age. Cardiac tissue was sampled for molecular analyses and assessment of cardiac structure and cardiomyocyte maturation. RESULTS: Lambs delivered preterm showed distinct ventricular differences in cardiomyocyte growth and maturation trajectories as well as remodeling of the left ventricular myocardium compared to fetal controls. Antenatal exposure to lipopolysaccharide resulted in further collagen deposition in the left ventricle and a greater presence of immune cells in the preterm heart. CONCLUSIONS: Adverse impacts of preterm birth on cardiac structure and cardiomyocyte growth kinetics within the first week of postnatal life are exacerbated by intrauterine inflammation. The maladaptive remodeling of the cardiac structure and perturbed cardiomyocyte growth likely contribute to the increased vulnerability to cardiac dysfunction following preterm birth. IMPACT: Preterm birth induces maladaptive cardiac remodeling and adversely impacts cardiomyocyte growth kinetics within the first week of life in sheep. These effects of prematurity on the heart are exacerbated when preterm birth is preceded by exposure to intrauterine inflammation, a common antecedent of preterm birth. Inflammatory injury to the fetal heart coupled with preterm birth consequently alters neonatal cardiac growth and maturation and thus, may potentially influence long-term cardiac function and health.

The cerebral haemodynamic response to somatosensory stimulation in preterm newborn lambs is reduced following intrauterine inflammation and dopamine infusion.

BACKGROUND: Neurovascular coupling leads to an increase in local cerebral blood flow and oxygenation in response to increased neural activity. Reduced cerebral functional responses may predispose to tissue hypoxia when neural activity is increased. Intrauterine inflammation, identified clinically as chorioamnionitis, is a major contributor to the neuropathology arising after preterm birth. The impact of chorioamnionitis on the preterm cerebral functional haemodynamic response is unknown. Previously, we have reported that somatosensory stimulation produces predominantly positive cerebral haemodynamic responses (i.e., increased cerebral oxygenation) in preterm lambs, which are reduced with dopamine treatment. As preterm infants born after chorioamnionitis often suffer from hypotension and are treated with dopamine, we aimed to investigate how chorioamnionitis with and without dopamine treatment affect the cerebral haemodynamic response in preterm lambs. METHODS: At 119 days of gestation, intrauterine inflammation was induced by intra-amniotic injection of lipopolysaccharide (LPS) in pregnant ewes. At 126-7 days of gestation (term is ~147 days), these LPS-exposed lambs were delivered and mechanically ventilated. The cerebral functional response was assessed by near infrared spectroscopy as changes in cerebral oxy- and deoxyhaemoglobin (ΔoxyHb, ΔdeoxyHb), following left median nerve stimulation of 1.8, 4.8 and 7.8 s durations without dopamine; and 4.8 and 7.8 s stimulations with intravenous dopamine infusion. RESULTS: Stimulation for 1.8, 4.8 and 7.8 s durations led to negative functional responses (decreased ΔoxyHb) in 5 (62.5%), 5 (62.5%) and 4 (50%) of 8 preterm lambs respectively, while other lambs showed positive responses (increased ∆oxyHb). Dopamine infusion increased baseline tissue oxygenation index (TOI), oxyHb and total Hb. In lambs with a positive functional response, dopamine decreased the evoked ΔoxyHb response, increasing the overall incidence of negative cerebral haemodynamic responses. CONCLUSIONS: Somatosensory stimulation produced mostly negative responses with decreased cerebral oxygenation in preterm lambs exposed to intrauterine inflammation, contrasting with our previous findings of predominantly positive responses in non-inflamed, control, preterm lambs. Dopamine increased baseline cerebral oxygenation, but further increased the incidence of negative functional responses. Impaired neurovascular coupling leading to intermittent localised tissue hypoxia may therefore contribute to the neuropathy in infants with chorioamnionitis, with the risk of injury exacerbated with dopamine treatment.

Interleukin-1 blockade attenuates white matter inflammation and oligodendrocyte loss after progressive systemic lipopolysaccharide exposure in near-term fetal sheep.

BACKGROUND: Increased systemic and tissue levels of interleukin (IL)-1ß are associated with greater risk of impaired neurodevelopment after birth. In this study, we tested the hypothesis that systemic IL-1 receptor antagonist (Ra) administration would attenuate brain inflammation and injury in near-term fetal sheep exposed to lipopolysaccharide (LPS). METHODS: Chronically instrumented near-term fetal sheep at 0.85 of gestation were randomly assigned to saline infusion (control, n = 9), repeated LPS infusions (0 h = 300 ng, 24 h = 600 ng, 48 h = 1200 ng, n = 8) or repeated LPS plus IL-1Ra infusions (13 mg/kg infused over 4 h) started 1 h after each LPS infusion (n = 9). Sheep were euthanized 4 days after starting infusions for histology. RESULTS: LPS infusions increased circulating cytokines and were associated with electroencephalogram (EEG) suppression with transiently reduced mean arterial blood pressure, and increased carotid artery perfusion and fetal heart rate (P < 0.05 vs. control for all). In the periventricular and intragyral white matter, LPS-exposure increased IL-1ß immunoreactivity, numbers of caspase 3+ cells and microglia, reduced astrocyte and olig-2+ oligodendrocyte survival but did not change numbers of mature CC1+ oligodendrocytes, myelin expression or numbers of neurons in the cortex and subcortical regions. IL-1Ra infusions reduced circulating cytokines and improved recovery of EEG activity and carotid artery perfusion. Histologically, IL-1Ra reduced microgliosis, IL-1ß expression and caspase-3+ cells, and improved olig-2+ oligodendrocyte survival. CONCLUSION: IL-1Ra improved EEG activity and markedly attenuated systemic inflammation, microgliosis and oligodendrocyte loss following LPS exposure in near-term fetal sheep. Further studies examining the long-term effects on brain maturation are now needed.

Postnatal inflammation in ApoE-/- mice is associated with immune training and atherosclerosis.

BACKGROUND AND AIMS: Preterm birth is associated with increased risk of cardiovascular disease (CVD). This may reflect a legacy of inflammatory exposures such as chorioamnionitis which complicate pregnancies delivering preterm, or recurrent early-life infections, which are common in preterm infants. We previously reported that experimental chorioamnionitis followed by postnatal inflammation has additive and deleterious effects on atherosclerosis in ApoE-/- mice. Here, we aimed to investigate whether innate immune training is a contributory inflammatory mechanism in this murine model of atherosclerosis. METHODS: Bone marrow-derived macrophages and peritoneal macrophages were isolated from 13-week-old ApoE-/- mice, previously exposed to prenatal intra-amniotic (experimental choriomanionitis) and/or repeated postnatal (peritoneal) lipopolysaccharide (LPS). Innate immune responses were assessed by cytokine responses following ex vivo stimulation with toll-like receptor (TLR) agonists (LPS, Pam3Cys) and RPMI for 24-h. Bone marrow progenitor populations were studied using flow cytometric analysis. RESULTS: Following postnatal LPS exposure, bone marrow-derived macrophages and peritoneal macrophages produced more pro-inflammatory cytokines following TLR stimulation than those from saline-treated controls, characteristic of a trained phenotype. Cytokine production ex vivo correlated with atherosclerosis severity in vivo. Prenatal LPS did not affect cytokine production capacity. Combined prenatal and postnatal LPS exposure was associated with a reduction in populations of myeloid progenitor cells in the bone marrow. CONCLUSIONS: Postnatal inflammation results in a trained phenotype in atherosclerosis-prone mice that is not enhanced by prenatal inflammation. If analogous mechanisms occur in humans, then there may be novel early life opportunities to reduce CVD risk in infants with early life infections.

The effect of human amnion epithelial cells on lung development and inflammation in preterm lambs exposed to antenatal inflammation.

BACKGROUND: Lung inflammation and impaired alveolarization are hallmarks of bronchopulmonary dysplasia (BPD). We hypothesize that human amnion epithelial cells (hAECs) are anti-inflammatory and reduce lung injury in preterm lambs born after antenatal exposure to inflammation. METHODS: Pregnant ewes received either intra-amniotic lipopolysaccharide (LPS, from E.coli 055:B5; 4mg) or saline (Sal) on day 126 of gestation. Lambs were delivered by cesarean section at 128 d gestation (term ~150 d). Lambs received intravenous hAECs (LPS/hAECs: n = 7; 30x106 cells) or equivalent volumes of saline (LPS/Sal, n = 10; or Sal/Sal, n = 9) immediately after birth. Respiratory support was gradually de-escalated, aimed at early weaning from mechanical ventilation towards unassisted respiration. Lung tissue was collected 1 week after birth. Lung morphology was assessed and mRNA levels for inflammatory mediators were measured. RESULTS: Respiratory support required by LPS/hAEC lambs was not different to Sal/Sal or LPS/Sal lambs. Lung tissue:airspace ratio was lower in the LPS/Sal compared to Sal/Sal lambs (P<0.05), but not LPS/hAEC lambs. LPS/hAEC lambs tended to have increased septation in their lungs versus LPS/Sal (P = 0.08). Expression of inflammatory cytokines was highest in LPS/hAECs lambs. CONCLUSIONS: Postnatal administration of a single dose of hAECs stimulates a pulmonary immune response without changing ventilator requirements in preterm lambs born after intrauterine inflammation.

Identification of placental androgen receptor isoforms in a sheep model of maternal allergic asthma.

Maternal asthma is known to impact intrauterine growth outcomes, which may be mediated, in part, by altered androgen signalling. Our aim was to explore whether the sheep placenta expresses androgen receptor (AR) isoforms and determine if the differential expression of AR protein isoforms is altered by maternal asthma. Four known AR isoforms were detected (AR-FL, AR-v1, AR-v7, and AR-45), and their expression and subcellular distribution was altered in the presence of maternal allergic asthma. These findings underscore the importance for in vivo models of maternal asthma to delineate molecular patterns that may contribute to feto-placental growth and development.

Brain inflammation and injury at 48 h is not altered by human amnion epithelial cells in ventilated preterm lambs.

BACKGROUND: Mechanical ventilation of preterm neonates is associated with neuroinflammation and an increased risk of adverse neurological outcomes. Human amnion epithelial cells (hAECs) have anti-inflammatory and regenerative properties. We aimed to determine if intravenous administration of hAECs to preterm lambs would reduce neuroinflammation and injury at 2 days of age. METHODS: Preterm lambs were delivered by cesarean section at 128-130 days' gestation (term is ~147 days) and either ventilated for 48 h or humanely killed at birth. Lambs received 3 mL surfactant (Curosurf) via endotracheal tube prior to delivery (either with or without 90 × 106 hAECs) and 3 mL intravenous phosphate-buffered saline (with or without 90 × 106 hAECs, consistent with intratracheal treatment) after birth. RESULTS: Ventilation increased microglial activation, total oligodendrocyte cell number, cell proliferation and blood-brain barrier permeability (P < 0.05, PBS + ventilation and hAEC + ventilation vs. control), but did not affect numbers of immature and mature oligodendrocytes. Ventilation reduced astrocyte and neuron survival (P < 0.05, PBS + ventilation and hAEC + ventilation vs. control). hAEC administration did not alter markers of neuroinflammation or injury within the white or gray matter. CONCLUSIONS: Mechanical ventilation for 48 h upregulated markers of neuroinflammation and injury in preterm lambs. Administration of hAECs did not affect markers of neuroinflammation or injury. IMPACT: Mechanical ventilation of preterm lambs for 48 h, in a manner consistent with contemporary neonatal intensive care, causes neuroinflammation, neuronal loss and pathological changes in oligodendrocyte and astrocyte survival consistent with evolving neonatal brain injury.Intravenous administration of hAECs immediately after birth did not affect neonatal cardiorespiratory function and markers of neuroinflammation or injury.Reassuringly, our findings in a translational large animal model demonstrate that intravenous hAEC administration to the preterm neonate is safe.Considering that hAECs are being used in phase 1 trials for the treatment of BPD in preterm infants, with future trials planned for neonatal neuroprotection, we believe these observations are highly relevant.

Hypothalamic hamartomas and inner ear diverticula with X-linked stapes gusher syndrome - new associations?

X-linked stapes gusher syndrome is a genetic form of deafness with distinct radiographic features on temporal bone CT. Hypothalamic hamartoma is a congenital glioneuronal anomaly of the hypothalamus. We report a potential association between these two rare anomalies that, to our knowledge, has not been reported. Two brothers presented with sensorineural hearing loss and almost identical inner ear and hypothalamic abnormalities, consistent with a diagnosis of X-linked stapes gusher syndrome and hypothalamic hamartoma. Genetic testing revealed identical mutations in the POU3F4 gene associated with X-linked stapes gusher syndrome. Furthermore, multiple vestibular diverticula were seen in both brothers, which have also not been reported with X-linked stapes gusher syndrome. This case suggests that POU3F4 mediated X-linked stapes gusher syndrome may also lead to multiple vestibular diverticula and hypothalamic hamartoma and, therefore, brain magnetic resonance imaging (MRI) could be considered in patients presenting with these inner ear findings.

Placental glucocorticoid receptor isoforms in a sheep model of maternal allergic asthma.

Maternal asthma increases the risk of adverse pregnancy outcomes and may affect fetal growth and placental function by differential effects on the expression of glucocorticoid receptor (GR) isoforms, leading to altered glucocorticoid signalling. Our aim was to examine the effect of maternal asthma on placental GR profiles using a pregnant sheep model of asthma. Nine known GR isoforms were detected. There was a significant increase in the expression of placental GR isoforms that are known to have low trans-activational activity in other species including GR A, GR P and GRγ which may result in a pro-inflammatory environment in the presence of allergic asthma.

Maternal allergic asthma during pregnancy alters fetal lung and immune development in sheep: potential mechanisms for programming asthma and allergy.

KEY POINTS: Experimental maternal allergic asthma in sheep provides an experimental model in which to test impacts on progeny. Fetuses from allergic asthmatic ewes had fewer surfactant-producing cells in lungs. A greater proportion of lymphocytes from thymus were CD44 positive in fetuses from allergic asthmatic ewes than in controls. These changes to fetal development might contribute to poor neonatal lung function and increased risk of allergy seen in offspring of pregnancies complicated by asthma. ABSTRACT: Asthma is prevalent in pregnancy and increases the risk of disease in offspring, including neonatal respiratory distress and childhood asthma and allergy, but the mechanisms are not understood. We hypothesized that fetal lung structure and immune phenotype in late gestation fetal sheep would be impaired in our sheep model of maternal allergic asthma during pregnancy. Singleton-bearing ewes were either sensitized before pregnancy to house dust mite (HDM, allergic, n = 7) or were non-allergic (control, n = 5). The ewes were subsequently subjected to repeated airway challenges with HDM (allergic group) or saline (control group) throughout gestation. Tissues were collected at 140 ± 1 days gestational age (term, ∼147 days). The density of type II alveolar epithelial cells (surfactant protein C-immunostained) in the lungs was 30% lower in fetuses from allergic ewes than in controls (P < 0.001), but tissue-to-air space ratio and numbers of leucocytes and macrophages were not different between groups. The proportion of CD44+ lymphocytes in the fetal thymus was 3.5-fold higher in fetuses from allergic ewes than in control ewes (P = 0.043). Fewer surfactant-producing type II alveolar epithelial cells may contribute to the increased risk of neonatal respiratory distress in infants of asthmatic mothers, suggesting that interventions to promote lung maturation could improve their neonatal outcomes. If the elevated lymphocyte expression of CD44 persists postnatally, this would confer greater susceptibility to allergic diseases in progeny of asthmatic mothers, consistent with observations in humans. Further experiments are needed to evaluate postnatal phenotypes of progeny and investigate potential interventions.

Postnatal inflammation following intrauterine inflammation exacerbates the development of atherosclerosis in ApoE-/- mice.

Atherosclerosis is a chronic inflammatory disease that has its origins in early life. Postnatal inflammation exacerbates atherosclerosis, but the possible effect of intrauterine inflammation is largely unexplored. Exposure to inflammation in utero is common, especially in infants born preterm, who have increased cardiovascular risk in adulthood. We hypothesised that exposure to inflammation before birth would accelerate the development of atherosclerosis, with the most severe atherosclerosis following exposure to both pre- and postnatal inflammation. Here we studied the effect of prenatal and postnatal inflammation on the development of atherosclerosis by combining established techniques for modelling histological chorioamnionitis and atherosclerosis using apolipoprotein E (ApoE) knockout mice. A single intra-amniotic (IA) injection of lipopolysaccharide (LPS) caused intrauterine inflammation, and increased atherosclerosis at 13 weeks of postnatal age. In mice exposed to postnatal LPS, chorioamnionitis modulated subsequent responses; atherosclerotic lesion size, number and severity were greatest for mice exposed to both intrauterine and postnatal inflammation, with a concomitant decrease in collagen content and increased inflammation of the atherosclerotic plaque. In conclusion, pre- and postnatal inflammation have additive and deleterious effects on the development of atherosclerosis in ApoE knockout mice. The findings are particularly relevant to preterm human infants, whose gestations are frequently complicated by chorioamnionitis and who are particularly susceptible to repeated postnatal infections. Human and mechanistic studies are warranted to guide preventative strategies.

Umbilical cord blood versus mesenchymal stem cells for inflammation-induced preterm brain injury in fetal sheep.

BACKGROUND: Chorioamnionitis and fetal inflammation are principal causes of neuropathology detected after birth, particularly in very preterm infants. Preclinical studies show that umbilical cord blood (UCB) cells are neuroprotective, but it is uncertain if allogeneic UCB cells are a feasible early intervention for preterm infants. In contrast, mesenchymal stem cells (MSCs) are more readily accessible and show strong anti-inflammatory benefits. We aimed to compare the neuroprotective benefits of UCB versus MSCs in a large animal model of inflammation-induced preterm brain injury. We hypothesized that MSCs would afford greater neuroprotection. METHODS: Chronically instrumented fetal sheep at 0.65 gestation received intravenous lipopolysaccharide (150 ng; 055:B5, n = 8) over 3 consecutive days; or saline for controls (n = 8). Cell-treated animals received 108 UCB mononuclear cells (n = 7) or 107 umbilical cord MSCs (n = 8), intravenously, 6 h after the final lipopolysaccharide dose. Seven days later, cerebrospinal fluid and brain tissue was collected for analysis. RESULTS: Lipopolysaccharide induced neuroinflammation and apoptosis, and reduced the number of mature oligodendrocytes. MSCs reduced astrogliosis, but UCB did not have the same effect. UCB significantly decreased cerebral apoptosis and protected mature myelinating oligodendrocytes, but MSCs did not. CONCLUSION: UCB appears to better protect white matter development in the preterm brain in response to inflammation-induced brain injury in fetal sheep.

Delivery of positive end-expiratory pressure to preterm lambs using common resuscitation devices.

BACKGROUND: In neonatal resuscitation, a ventilation device providing positive end-expiratory pressure (PEEP) is recommended. There is limited information about PEEP delivery in vivo, using different models of self-inflating bag (SIB) at different inflation rates and PEEP settings. METHODS: We compared PEEP delivery to intubated preterm lambs using four commonly available models of paired SIBs and PEEP valves, with a T-piece, with gas flow of 8 L/min. Peak inspiratory pressure inflations of 30 cmH2O, combined with set PEEP of 5, 7 and 10 cmH2O, were delivered at rates of 20, 40 and 60/min. These combinations were repeated without gas flow. We measured mean PEEP, maximum and minimum PEEP, and its difference (PEEP reduction). RESULTS: A total of 3288 inflations were analysed. The mean PEEP delivered by all SIBs was lower than set PEEP (P<0.001), although some differences were <0.5 cmH2O. In 55% of combinations, the presence of gas flow resulted in increased PEEP delivery (range difference 0.3-2 cmH2O). The mean PEEP was closer to set PEEP with faster inflation rates and higher set PEEPs. The mean (SD) PEEP reduction was 3.9 (1.6), 8.2 (1.8), 2 (0.6) and 1.1 (0.6) cmH2O with the four SIBs, whereas it was 0.5 (0.2) cmH2O with the T-piece. CONCLUSIONS: PEEP delivery with SIBs depends on the set PEEP, inflation rate, device model and gas flow. At recommended inflation rates of 60/min, some devices can deliver PEEP close to the set level, although the reduction in PEEP makes some SIBs potentially less effective for lung recruitment than a T-piece.

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.

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)-1ß, 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 Prior to Umbilical Cord Clamping Improves Cardiovascular Stability and Oxygenation in Preterm Lambs After Exposure to Intrauterine Inflammation.

Background: Delaying umbilical cord clamping until after aeration of the lung (physiological-based cord clamping; PBCC) maintains cardiac output and oxygenation in preterm lambs at birth, however, its efficacy after intrauterine inflammation is not known. Given the high incidence of chorioamnionitis in preterm infants, we investigated whether PBCC conferred any benefits compared to immediate cord clamping (ICC) in preterm lambs exposed antenatally to 7 days of intrauterine inflammation. Methods: Ultrasound guided intraamniotic injection of 20 mg Lipopolysaccharide (from E. coli:055:B5) was administered to pregnant ewes at 0.8 gestation. Seven days later, ewes were anesthetized, preterm fetuses exteriorised via cesarean section, and instrumented for continuous measurement of pulmonary, systemic and cerebral pressures and flows, and systemic, and cerebral oxygenation. Lambs were then randomized to either PBCC, whereupon ventilation was initiated and maintained for 3 min prior to umbilical cord clamping, or ICC where the umbilical cord was cut and ventilation initiated 30 s later. Ventilation was maintained for 30 min. Results: ICC caused a rapid fall in systemic (by 25%) and cerebral (by 11%) oxygen saturation in ICC lambs, concurrent with a rapid increase in carotid arterial pressure and heart rate. The overshoot in carotid arterial pressure was sustained in ICC lambs for the first 20 min of the study. PBCC maintained cardiac output and prevented the fall in cerebral oxygen delivery at birth. PBCC lambs had lower respiratory compliance and higher respiratory requirements throughout the study. Conclusion: PBCC mitigated the adverse effects of ICC on oxygenation and cardiac output, and therefore could be more beneficial in preterm babies exposed to antenatal inflammation as it maintains cardiac output and oxygen delivery. The increased respiratory requirements require further investigation in this sub-group of preterm infants.

Improving pregnancy outcomes in humans through studies in sheep.

Experimental studies that are relevant to human pregnancy rely on the selection of appropriate animal models as an important element in experimental design. Consideration of the strengths and weaknesses of any animal model of human disease is fundamental to effective and meaningful translation of preclinical research. Studies in sheep have made significant contributions to our understanding of the normal and abnormal development of the fetus. As a model of human pregnancy, studies in sheep have enabled scientists and clinicians to answer questions about the etiology and treatment of poor maternal, placental, and fetal health and to provide an evidence base for translation of interventions to the clinic. The aim of this review is to highlight the advances in perinatal human medicine that have been achieved following translation of research using the pregnant sheep and fetus.