Short- and long-term respiratory complications of premature birth are significant sources of illness and financial burden in the United States, and their impact is only increasing. With this in mind, the National Institutes of Health (NIH) and the National Heart, Lung, and Blood Institute (NHLBI) recently funded a new 5-year $18.5 million research initiative to improve understanding of and improve strategies for managing the respiratory complications of premature and low birth weight infants.
Awarded in May 2010, the Prematurity and Respiratory Outcomes Program (PROP) is designed to uncover molecular mechanisms that contribute to acute and chronic respiratory morbidity in a multicenter cohort of premature infants. The program seeks to understand similarities and differences among premature neonates that correlate with future risk for respiratory morbidity; identify objective biomarkers and outcome measures of respiratory morbidity in this population; identify novel mechanisms of neonatal lung disease; and identify potential therapeutic targets in at-risk subjects.
The NHLBI has provided funding to five neonatal clinical research centers—Cincinnati Children’s Hospital Medical Center; Washington University in St Louis (WUSTL); Vanderbilt University, Nashville, Tenn; the University of California, San Francisco (UCSF); and the University of Rochester and University of Buffalo, New York State. Funding is also included for a Data Coordinating Center, which will coordinate the research of the five research centers and oversee the biorepository.
PROP has also received additional funds from the National Institute of Child Health and Human Development’s Best Pharmaceutical for Children’s Act Initiative to collect detailed data on the medications currently being prescribed for very preterm infants during the first year of life. This data will be used to inform the design of future clinical research studies and shape evidence-based practice guidelines for this at-risk population.
For Aaron Hamvas, MD, professor of pediatrics and director of clinical affairs for newborn medicine at WUSTL, the PROP initiative is important because it allows researchers to take advantage of new, sophisticated research tools. Recent advances in biomedical technology now make it possible to analyze cells, genes, proteins, and metabolites in very small volumes of biologic specimens. In addition, advances in methods to measure infant physiology, and in data management and computer analysis, offer new opportunities for researchers involved with the PROP.
In addition, the lack of progress over the last 20 years in really understanding this disorder underscores the importance of the PROP initiative for Hamvas.
“This has been a problem that has plagued neonatologists and, quite frankly, premature babies since neonatology came into existence, and we still don’t really understand it,” he says. “[This is an opportunity] to get in there and understand more so we can prevent it, have better treatment, or really help families anticipate what they’re in for long term.”
For Gloria Pryhuber, MD, associate professor of pediatrics and environmental medicine at the University of Rochester, the PROP’s emphasis on better defining biomarkers for infants at greatest risk for respiratory morbidity will help physicians better manage these infants long term.
“PROP will identify objective measures that can be used to predict premature newborns who will have persistent respiratory problems over the first year after neonatal intensive care unit discharge. With these measures and an understanding of outcomes, we can make better-informed management choices for children,” Pryhuber adds.
Each year in the United States, more than 550,000 babies are born prematurely, before 37 completed weeks of gestation. Rates of premature birth have also been increasing—10.6% in 1990, 12.8% in 2006, and a 30% increase since 1981—making efforts to understand and improve strategies for managing premature and low birth weight infants an important public health goal.
According to Pryhuber, babies born at less than 38 weeks of gestation are at risk for significant respiratory morbidity, especially during the first year of life. They return to pediatricians, emergency departments, and pulmonologists with symptomatic respiratory dysfunction (SRD), intermittent or chronic wheezing, poor growth, and lower respiratory tract infections. Of those born at 22 to 29 weeks of gestation, 35% to 45% develop the chronic lung disease, bronchopulmonary dysplasia (BPD), defined as a continued need for oxygen therapy as the infant reaches 36 weeks corrected gestational age. BPD itself is a nonspecific diagnosis based on a supplemental oxygen requirement at 36 weeks of postmenstrual age (PMA), and is likely caused by more than one mechanism. According to the NHLBI, the pathophysiology that contributes to respiratory morbidity may include airway obstruction, low lung volumes due to abnormal alveolarization, pulmonary hypertension, or apnea. Given that infants currently are not separated by objective measures to phenotype the underlying respiratory limitation, the NHLBI, and the heart of the PROP initiative, contends that better understanding of the different mechanisms and the characteristics of the premature infants associated with each mechanism would permit stratification of risk, better informed therapeutic choices, and, possibly, markers for evaluating risk modification.
The annual cost of treating infants with BPD is greater than $2.5 billion, second to treatment of asthma, but exceeding costs of treating cystic fibrosis. Airway function also may further deteriorate during the first year of life in infants with BPD. Studies at adolescence suggest persistent, and deteriorating, COPD-like pulmonary dysfunction in children born prematurely.
“If this is the case,” Pryhuber says, “then the costs of managing lung disease of prematurity will exceed well into adulthood.”
Despite greater survival at ever-younger gestational ages, the fact remains that premature infants, especially those with BPD, are at risk for growth failure, thought to further impair lung growth and development. Moreover, additional data now suggests evidence of emphysema, potentially progressive, in adolescence and adulthood, according to Pryhuber.
“Nothing we’ve done has really made a dent on the incidence of BPD. Twenty years ago, it was bigger babies who got BPD; now those babies don’t seem to get BPD as much, but the incidence of BPD has not fallen because we have smaller and smaller babies surviving who still go on to develop BPD,” says Judy Aschner, MD, professor of pediatrics and neonatology at Vanderbilt.
Pulling Together Expertise
While chronic lung disease is often talked about as a single problem, the reality, according to Hamvas, is that it is many different things, and no one person can understand it. The PROP provides the opportunity, he says, to pool the expertise of the five participating centers—including the genetic expertise at WUSTL and the immunological expertise of Rochester/Buffalo and Cincinnati—to improve the field’s understanding of the problem.
“Utilizing the strengths of the individual centers and pooling those strengths really adds a new dimension for how to approach this problem,” Hamvas says.
Aschner agrees. “This is an area where we’ve struggled to make headway, but really have not had a dramatic impact on the overall incidence of this disease,” she says. “The PROP RFA that was released by the NHLBI really caught my attention because it wasn’t starting out the door saying let’s try another randomized control trial of some intervention that we hope will work, but rather let’s go back to fundamentals. Let’s define this disease in a much more sophisticated way. We have new tools and new ways of thinking about it. Let’s find a better way to phenotype these infants.”
Aschner’s team at Vanderbilt plans to investigate interrelated pathways associated with chronic lung disease—the urea cycle-nitric oxide (UC-NO) and glutathione (GSH) pathways. They hope to determine which biomedical, clinical, and genetic factors affecting these pathways are associated with more severe BPD and persistent pulmonary disease (PPD) phenotypes, using multivariable regression modeling and machine learning. The team hypothesizes that measurable differences in UC-NO intermediates and GSH precursors result, in preterm infants, from biochemical immaturity, genetic variation, and an adverse environment that increase demands and reduce the synthetic capacity of these systems and that the duration and degree of NO insufficiency and free radical excess modulate the persistence of pulmonary disease in premature infants.
Pryhuber’s team at Rochester/Buffalo, meanwhile, will capitalize on long-standing interests and research efforts directed toward understanding lung injury and abnormal repair occurring after premature birth and resulting in BPD. The team will focus on understanding how premature birth alters the development of lymphocytes, especially the cytotoxic T cells that are important in protection against viral infections and that may contribute to inflammatory lung disease in premature babies. According to Pryhuber, the team hypothesizes that premature birth alters cellular immune maturation and function, contributing to susceptibility to viral infections and promoting cytotoxic lung damage and respiratory sequelae.
The project will utilize high-throughput, multiparameter flow cytometry to evaluate the development of adaptive immune cells in the blood of a prospective cohort of 180 premature infants, in comparison to a small group of term infants. Blood samples will be analyzed at birth, at NICU discharge, and at 1 year of life. Lymphocyte phenotypes will be analyzed particularly in the context of gestational age and maternal-fetal and newborn stressors capable of modulating oxidative stress (oxygen exposure, infection, and environmental tobacco smoke exposure) and inflammation. Peripheral lymphocyte, lineage-specific, transcriptomic approaches, genome-wide expression studies, and immune-phenotyping data will be applied to the prediction of respiratory outcomes of the premature.
Taking advantage of WUSTL’s Genome Sequencing Center and its participation in the Human Microbiome Project, Hamvas’ team seeks to determine differences in the composition of the intestinal microbiota between groups of premature newborns and evaluate associations between the identity of specific enteric microbiome signatures and the risk and severity of BPD. The team plans to use shotgun sequencing of microbial DNA to identify differences in the metagenomic and/or transcriptional repertoire of the enteric microbiota between groups of premature newborns and evaluate their association with risk and severity of BPD.
“What we would hope to find is that there is some relationship between the bacterial genes that are being expressed in the premature baby and the occurrence and/or severity of BPD,” says Hamvas. If such a link can be found, Hamvas hopes future research can look at modulating this interaction through additional antibiotics or some other kind of molecules. “The question,” according to Hamvas, “is whether you can influence the bacterial composition of the intestinal tract so that the good genes are being expressed rather than the deleterious genes.”
The team at UCSF, led by Roberta Keller, MD, assistant professor of clinical pediatrics and medical director of the Neonatal ECMO Program, meanwhile, plans to collect and analyze tracheal aspirates and urine samples for biomarkers that correlate and predict long-term respiratory outcomes at 1 year of age. They hypothesize that respiratory status at 1 week (requirement for mechanical ventilation) and at 40 weeks PMA (requirement for supplemental oxygen or ventilator support), low content of SP-B and increased levels of selected inflammatory cytokines in lung fluid in the first week of life, and low levels of lung nitric oxide production and turnover of elastin, as reflected by excretion of urinary NO metabolites/cGMP and desmosine, respectively, serve as biomarkers and robust predictors of pulmonary outcome at 1 year.
“One of the things I’ve been very interested in is looking at urine biomarkers because urine is easy to collect and a very low [participation] barrier for families,” Keller says. “[Urine] is something that you can follow in kids when they are very sick, when they are very well, as they are getting ready for discharge, and potentially even after they are discharged. That gives you the opportunity to study a broad group of patients with a source that isn’t dependent on a certain state of the patient.”
Researchers at Cincinnati Children’s Hospital Medical Center, led by Alan Jobe, MD, PhD, professor of pediatrics at the University of Cincinnati College of Medicine, plan to sample blood, gastric aspirates, tracheal aspirates, and saliva to test a number of hypotheses, including that sustained and uncontrolled pro-inflammatory Th17 lymphocytic activation occurs in BPD, that salivary glycan phenotype and secretor genotype predict severe BPD and BPD case fatality in extremely low birth weight neonates, and that SP-A and SP-D production at birth and subsequent plasma SP-A and SP-D levels are biomarkers for subsequent development of BPD.
“I have no idea if we are going to identify useful biomarkers, but at least we’ll learn something more about the disease. This is really a complicated disease that is both injury repair and development all piled up on top of each other. So there’s no magic bullet,” Jobe says.
Power of Numbers
An additional component of the PROP is the creation of a database and biorepository of approximately 750 premature infants, comprised of participants from each of the five sites, and available to collaborating sites.
Subjects born at less than 28 weeks of gestation will be monitored for respiratory morbidity, including a novel, multifaceted assessment of respiratory status at time of NICU discharge. Comprehensive 1-year respiratory outcomes assessments will record respiratory symptoms, resource utilization, medication prescribing and use patterns, and a focused physical exam at 12 months corrected gestational age. The participating centers also will provide for comparison analyses of multiple potential biomarkers, measurable in samples of blood, urine, tracheal aspirates, and saliva of preterm infants.
Although BPD is common among preterm infants, the reality is that compared to adult studies, neonatal studies are always small.
“We can’t enroll 10,000 infants [who are] less than 29 weeks. They just aren’t there,” Aschner says. “So pulling together five large clinical sites that have good infrastructure for doing this kind of clinical research really adds power. It’s still not tens of thousands, but a lot more than any one site that might enroll 150 or 200 babies would have.”
Eventually, the database and biorepository will be made more broadly available to the scientific community.
Blazing New Ground
For the five centers participating in the PROP, the NIH initiative stands out as a truly novel opportunity.
“To have five single center studies funded that are all looking at different things—some are looking at immunology, some are looking at biochemistry, some are looking at the stool and the microbiome—they’re really creative, different studies,” says Aschner. “In and of itself, [the PROP] is going to be a treasure trove of information and then to combine the power across all five sites to get that many babies for phenotyping and for looking at biomarkers is just a really novel idea.
“I think we are blazing new ground with this RFA,” adds Aschner. “It’s an experiment. I truly don’t know of another study group or program that looks like PROP. But if it’s successful, it might be a model for how other chronic problems that have had little progress [made in treating them] might be approached by the NIH.”
Alison Werner is associate editor for RT. For further information, contact [email protected]