Postnatal changes in lung phospholipids and alveolar macrophages in term newborn monkeys

Analysis of the regulation of surfactant phosphatidylcholine metabolism using stable isotopes

The pathways and mechanisms that regulate pulmonary surfactant synthesis, processing, secretion and catabolism have been extensively characterised using classical biochemical and analytical approaches. These have constructed a model, largely in experimental animals, for surfactant phospholipid metabolism in the alveolar epithelial cell whereby phospholipid synthesised on the endoplasmic reticulum is selectively transported to lamellar body storage vesicles, where it is subsequently processed before secretion into the alveolus. Surfactant phospholipid is a complex mixture of individual molecular species defined by the combination of esterified fatty acid groups and a comprehensive description of surfactant phospholipid metabolism requires consideration of the interactions between such molecular species. However, until recently, lipid analytical techniques have not kept pace with the considerable advances in understanding of the enzymology and molecular biology of surfactant metabolism. Refinements in electrospray ionisation mass spectrometry (ESI-MS) can now provide very sensitive platforms for the rapid characterisation of surfactant phospholipid composition in molecular detail. The combination of ESI-MS and administration of phospholipid substrates labelled with stable isotopes extends this analytical approach to the quantification of synthesis and turnover of individual molecular species of surfactant phospholipid. As this methodology does not involve radioactivity, it is ideally suited to application in clinical studies. This review will provide an overview of the metabolic processes that regulate the molecular specificity of surfactant phosphatidylcholine together with examples of how the application of stable isotope technologies in vivo has, for the first time, begun to explore regulation of the molecular specificity of surfactant synthesis in human subjects.

Progressive Vascular Functional and Structural Damage in a Bronchopulmonary Dysplasia Model in Preterm Rabbits Exposed to Hyperoxia

Bronchopulmonary dysplasia (BPD) is caused by preterm neonatal lung injury and results in oxygen dependency and pulmonary hypertension. Current clinical management fails to reduce the incidence of BPD, which calls for novel therapies. Fetal rabbits have a lung development that mimics humans and can be used as a translational model to test novel treatment options. In preterm rabbits, exposure to hyperoxia leads to parenchymal changes, yet vascular damage has not been studied in this model. In this study we document the early functional and structural changes of the lung vasculature in preterm rabbits that are induced by hyperoxia after birth. Pulmonary artery Doppler measurements, micro-CT barium angiograms and media thickness of peripheral pulmonary arteries were affected after seven days of hyperoxia when compared to controls. The parenchyma was also affected both at the functional and structural level. Lung function testing showed higher tissue resistance and elastance, with a decreased lung compliance and lung capacity. Histologically hyperoxia leads to fewer and larger alveoli with thicker walls, less developed distal airways and more inflammation than normoxia. In conclusion, we show that the rabbit model develops pulmonary hypertension and developmental lung arrest after preterm lung injury, which parallel the early changes in human BPD. Thus it enables the testing of pharmaceutical agents that target the cardiovascular compartment of the lung for further translation towards the clinic.

Four decades of leading-edge research in the reproductive and developmental sciences: the Infant Primate Research Laboratory at the University of Washington National Primate Research Center

The Infant Primate Research Laboratory (IPRL) was established in 1970 at the University of Washington as a visionary project of Dr. Gene (Jim) P. Sackett. Supported by a collaboration between the Washington National Primate Research Center and the Center on Human Development and Disability, the IPRL operates under the principle that learning more about the causes of abnormal development in macaque monkeys will provide important insights into the origins and treatment of childhood neurodevelopmental disabilities. Over the past 40 years, a broad range of research projects have been conducted at the IPRL. Some have described the expression of normative behaviors in nursery-reared macaques while others have focused on important biomedical themes in child health and development. This article details the unique scientific history of the IPRL and the contributions produced by research conducted in the laboratory. Past and present investigations have explored the topics of early rearing effects, low-birth-weight, prematurity, birth injury, epilepsy, prenatal neurotoxicant exposure, viral infection (pediatric HIV), diarrheal disease, vaccine safety, and assisted reproductive technologies. Data from these studies have helped advance our understanding of both risk and resiliency in primate development. New directions of research at the IPRL include the production of transgenic primate models using our embryonic stem cell-based technology to better understand and treat heritable forms of human intellectual disabilities such as fragile X.

Regulation of lung surfactant phospholipid synthesis and metabolism

The alveolar type II epithelial (ATII) cell is highly specialised for the synthesis and storage, in intracellular lamellar bodies, of phospholipid destined for secretion as pulmonary surfactant into the alveolus. Regulation of the enzymology of surfactant phospholipid synthesis and metabolism has been extensively characterised at both molecular and functional levels, but understanding of surfactant phospholipid metabolism in vivo in either healthy or, especially, diseased lungs is still relatively poorly understood. This review will integrate recent advances in the enzymology of surfactant phospholipid metabolism with metabolic studies in vivo in both experimental animals and human subjects. It will highlight developments in the application of stable isotope-labelled precursor substrates and mass spectrometry to probe lung phospholipid metabolism in terms of individual molecular lipid species and identify areas where a more comprehensive metabolic model would have considerable potential for direct application to disease states.

Age-dependent changes in porcine alveolar macrophage function during the postnatal period of alveolarization

During early postnatal ontogeny in most mammals, the lung is structurally and functionally immature. In some species with relatively altricial lung morphology, there is evidence of a coupling between functional maturity of the pulmonary cellular immune system and alveolar maturation. Herein, we examine changes in alveolar macrophage (AM) number and function occurring during alveolarization in a more precocial species, the pig, to determine if heightened oxidative metabolism and phagocytic ability is similarly delayed until completion of lung morphogenesis. We assessed cell differential in lavage fluid and evaluated two main functional parameters of AM phagocytic response, the generation of reactive oxygen species (ROS), and particle internalization. AM functional maturation occurred mainly during the first postnatal week: the proportion of AMs, ROS generation, and phagocytosis all increased significantly. These results suggest maturational improvement of the impaired AM-based pulmonary immune system of the neonate piglet occurs during the postnatal period of rapid alveolarization.

Perinatal tuberculosis: new challenges in the diagnosis and treatment of tuberculosis in infants and the newborn

With increasing rates of tuberculosis (TB) infection and disease worldwide, the rate of perinatal TB is also affected. A high index of suspicion by health professionals, in both the developed and developing world, is required to detect and manage tuberculosis in pregnancy and the early newborn period. Differences in immune responses in the fetus and neonate add to the diagnostic difficulties already recognised in young children. Although specific guidelines for the treatment of this potentially devastating disease are lacking due to paucity of experience, outcome is favourable, if the condition is recognised and treated according to existing TB protocols. HIV co-infection, multi- and extensively-drug resistant (MDR/XDR) TB contribute to the challenges. New diagnostic and vaccine developments hold future promise, but much work is needed to completely understand the complex immune responses to tuberculosis and control this disease.

Paediatric tuberculosis

Tuberculosis continues to cause an unacceptably high toll of disease and death among children worldwide, particularly in the wake of the HIV epidemic. Increased international travel and immigration have led to a rise in childhood tuberculosis rates even in traditionally low burden, industrialised settings, and threaten to promote the emergence and spread of multidrug-resistant strains. Whereas intense scientific and clinical research efforts into novel diagnostic, therapeutic, and preventive interventions have focused on tuberculosis in adults, childhood tuberculosis has been relatively neglected. However, children are particularly vulnerable to severe disease and death following infection, and those with latent infection become the reservoir for future transmission following disease reactivation in adulthood, fuelling future epidemics. Further research into the epidemiology, immune mechanisms, diagnosis, treatment, and prevention of childhood tuberculosis is urgently needed. Advances in our understanding of tuberculosis in children would provide insights and opportunities to enhance efforts to control this disease.

The composition of pulmonary surfactant from diving mammals

Maintaining a functional pulmonary surfactant system at depth is critical for diving mammals to ensure that inspiration is possible upon re-emergence. The lipid and protein composition of lavage extracts from three pinniped species (California sea lion, Northern elephant seal and Ringed seal) were compared to several terrestrial species. Lavage samples were purified using a NaBr discontinuous gradient. Concentrations of phospholipid classes and molecular species were measured using electrospray ionisation mass spectrometry, cholesterol was measured using high-performance liquid chromatography, surfactant protein A (SP-A) and SP-B were measured using enzyme-linked immunosorbent assays. There were small differences in phospholipid classes, with a lower level of anionic surfactant phospholipids, PG and PI, between diving and terrestrial mammals. There were no differences in PL saturation or SP-A levels between species. PC16:0/14:0, PC16:0/16:1, PC16:0/16:0, long chain PI species and the total concentrations of alkyl-acyl species of PC and PG as a ratio of diacyl species were increased in diving mammals, whereas concentrations of PC16:0/18:1, PG16:0/16:0 and PG16:0/18:1 were decreased. Cholesterol levels were very variable between species and SP-B was very low in diving mammals. These differences may explain the very poor surface activity of pinniped surfactant that we have previously described [Miller, N.J., Daniels, C.B., Schürch, S., Schoel, W.M., Orgeig, S., 2005. The surface activity of pulmonary surfactant from diving mammals. Respir. Physiol. Neurobiol. 150 (2006) 220-232], supporting the hypothesis that pinniped surfactant has primarily an anti-adhesive function to meet the challenges of regularly collapsing lungs.

Comparison of the pulmonary surfactant content in alveolar macrophages of newborn, young, and adult rats

The phospholipid composition of the 150-g pellet containing macrophages from neonatal lung lavages resembles that of surfactant. To study whether this composition reflects the surfactant content of the macrophage, we isolated the alveolar phospholipids and macrophages from the lavage fluids of fetal, newborn, young, and adult Wistar rats. The alveolar surfactant phospholipids increased from fetal levels of 2.8 nmol/mg dry lung weight (DLW) to 39 nmol/mg DLW at day 1, decreased sharply within the first week, and stabilized at a level of 2-4 nmol/mg DLW after day 15. The number of alveolar macrophages increased significantly during the first postnatal day from approximately 750 to more than 5000 (per mg DLW), decreased during the next 4 days, and varied strongly at older ages. We estimated the surfactant content in the macrophages semiquantitatively by polarization microscopy. Birefringence augmented significantly during the first 1.5 days after birth and decreased after that concurrently with the amount of alveolar surfactant. However, only cells without birefringent inclusions sedimented at 150g, whereas the phospholipid composition of the pellets falsely suggested that large amounts of intracellular surfactant were present in its cells. At least two populations of macrophages (surfactant-rich and surfactant-poor) are present in the growing animal. We suggest that differences in function of these various types of macrophages also might depend on surfactant congestion.