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Anna Penn

Protecting the fetal brain from harm

Anna Penn

Ongoing placental dysfunction and allopregnanolone loss, not the increase that was expected due to stress, may alter cortical development in complicated pregnancies and put babies at risk, says Anna Penn, M.D., Ph.D.

Researchers long have known that allopregnanolone (ALLO), a derivative of the hormone progesterone, is produced in adults’ brains during times of acute stress and modulates how easily the brain’s neurons fire. ALLO also is produced in the placenta during fetal development, one of more than 200 different hormones that each uniquely contribute to fostering a smooth pregnancy and maintaining a fetus’ overall health. Although ALLO is thought to protect the developing brain in pregnancies complicated by conditions that might harm it, such as high blood pressure, how its levels evolve during pregnancy and in newborns shortly after birth has remained unknown.

Now, a new study presented during the Pediatric Academic Societies (PAS) 2018 annual meeting suggests that the placenta ramps up ALLO production over the second trimester, peaking just as fetuses approach full term.

To investigate this phenomenon, Anna Penn, M.D., Ph.D., a neonatologist/neuroscientist at Children’s National Health System, and colleagues created a designer experimental model to study how premature loss of ALLO alters orderly brain development. Knowing more about the interplay between ALLO and normal development of the cortex, the outer layer of the cerebrum, is a first step that could lead to strategies to rescue this vital brain region.

“The cortex is basically the brain’s command-and-control center for higher functions. In our experimental model, it develops from the middle of gestation through to the end of gestation. If ALLO levels are disrupted just as these cells are being born, neurons migrating to the cortex are altered and the developing neural network is compromised,” says Dr. Penn, senior author of the research presented at PAS 2018. “We’re concerned this same phenomenon occurs in human infants whose preterm birth disrupts their supply of this essential hormone.”

To better understand the human placental hormone pattern, the research team analyzed cord blood or serum samples collected within the first 36 hours of life for 61 preterm newborns born between 24 to 36 gestational weeks. They compared those preemie samples with samples drawn from 61 newborns carried to term who were matched by race, gender, size for gestational age, delivery method and maternal demographics.

They used liquid-chromatography-tandem mass spectrometry, a technique that can precisely analyze trace levels of compounds, to compare levels of 27 different steroids, including ALLO and its precursors as well as better-known adrenal gland hormones, such as cortisol and 17-Hydroxyprogesterone.

“Pregnancies complicated by hypertension tended to correlate with lower ALLO levels, though this finding did not reach statistical significance. This suggests that ongoing placental dysfunction and ALLO loss, not the increase that we expected to be caused by stress, may alter cortical development in these pregnancies and put babies at risk,” Dr. Penn adds. “In addition, having the largest neonatal sample set to date in which multiple steroid hormones have been measured can provide insight into the shifting hormone patterns that occur around 36 weeks gestation, just prior to term. Hopefully, restoring the normal hormonal milieu for preemies or other at-risk newborns will improve neurological outcomes in the future.”

In addition to Dr. Penn, study co-authors include Caitlin Drumm, MedStar Georgetown University Hospital; Sameer Desale, MedStar Health Research Institute; and Kathi Huddleston, Benjamin Solomon and John Niederhuber, Inova Translational Medicine Institute.

Sudeepta Basu

GABA concentration in pre-term brain increases with gestational age

Sudeepta Basu

“A more complete understanding of the diagnostic and prognostic importance of GABA and glutamate in the preterm brain will help us to direct treatment strategies for the most vulnerable preterm infants at risk of brain injury,” says Sudeepta K. Basu, M.D.

The major neurotransmitters gamma-aminobutyric acid (GABA) and glutamate are pivotal to fetal and newborn brain development and influence evolution of brain injury and repair following preterm birth. Magnetic resonance spectroscopy (MRS) enables in vivo measurement of brain metabolites. However, GABA and glutamate are found in the developing brain in low concentrations, and their weak signal can be swamped by the stronger signal of more dominant metabolites.

A Children’s research team reports findings from a pilot study utilizing an innovative technique of MRS to reliably measure in vivo GABA in the developing preterm brain. The groundbreaking research done by the team that includes Principal Investigator Sudeepta K. Basu, M.D., neonatology attending at Children’s National Health System, is very unique and original since there are no existing data of in vivo GABA concentrations in the developing cerebellum. Under the mentorship of Catherine Limperopoulos, Ph.D., director of Children’s Developing Brain Research Laboratory, the team of multi-disciplinary specialists is pursuing cutting-edge technologies in advanced MRI neuroimaging to explore brain development and injury in preterm infants.

The research, presented at the Eastern Society for Pediatric Research (ESPR) annual meeting by Dr. Basu, was honored with the “2018 Meritorious Poster Award.” The research titled “Distinct temporal trends of GABA and glutamate in the cerebellum and frontal cortex of preterm infants” reports, for the first time, positive temporal trends in the specific regions of the developing brain intricately involved in cognitive and motor functions. This work lays the foundation for developing novel ways to diagnose, monitor and investigative brain protective therapies for vulnerable prematurely born infants.

The Children’s team performed non-sedated MRS in 44 preterm infants whose mean gestational age at birth was 26.5 weeks, placing voxels at the middle of the cerebellum and the right frontal cortex. GABA and GIx (glutamate combined with glutamine) were positively correlated with post-menstrual age in the frontal cortex, but not the cerebellum.  At the ESPR meeting, the team also presented for the first time that caffeine, a neuroprotective agent in preemies, leads to increased in vivo GABA concentration in the developing frontal cortex.

“Open questions include whether these findings reflect varying paces of maturation and vulnerability to injury among specific regions of the brain. Also, the relationship between clinical factors and medication exposure and changes in the concentration of these neurotransmitters may guide brain protective therapies in future,” Dr. Basu says. “A more complete understanding of the diagnostic and prognostic importance of GABA and glutamate in the preterm brain will help us to direct treatment strategies for the most vulnerable preterm infants at risk of brain injury.”

Children’s senior fellows from Division of Neonatology made four platform presentations during the ESPR conference:

  • “Caffeine increases GABA/Cr ratio in frontal cortex of preterm infants on spectroscopy.” Aditi Gupta; Sudeepta K. Basu, M.D.; Mariam Said, M.D.; Subechhya Pradhan, Linda White; Kushal Kapse; Jonathan Murnick, M.D., Ph.D.; Taeun Chang, M.D.; and Catherine Limperopoulos, Ph.D.
  • “Impact of early nutrition on microstructural brain development in VLBW Infants.” Katherine M. Ottolini, Nickie Andescavage, M.D.; Kushal Kapse; and Catherine Limperopoulos, Ph.D.
  • “Direct measurement of neonatal cardiac output utilizing the CO status monitor.” Simranjeet S. Sran, Mariam Said, M.D.; and Khodayar Rais-Bahrami, M.D.
  • “Cerebro-cerebellar diaschisis in preterm infants following unilateral cerebral parenchymal injury.” Huma Mirza, Yao Wu, Kushal Kapse, Jonathan Murnick, M.D., Ph.D.; Taeun Chang, M.D.; and Catherine Limperopoulos, Ph.D.

Setting a baseline for healthy brain development

Catherine Limperopoulos, Ph.D., and colleagues performed the largest magnetic resonance imaging study of normal fetal brains in the second and third trimesters of pregnancy.

Starting as a speck barely visible to the naked eye and ending the in utero phase of its journey at an average weight of 7.5 pounds, the growth of the human fetus is one of the most amazing events in biology. Of all the organs, the fetal brain undergoes one of the most rapid growth trajectories, expanding over 40 weeks from zero to 100 billion neurons — about as many brain cells as there are stars in the Milky Way Galaxy.

This exponential growth is part of what gives humans our unique abilities to use language or have abstract thoughts, among many other cognitive skills. It also leaves the brain extremely vulnerable should disruptions occur during fetal development. Any veering off the developmental plan can lead to a cascade of results that have long-lasting repercussions. For example, studies have shown that placental insufficiency, or the inability of the placenta to supply the fetus with oxygen and nutrients in utero, is associated with attention deficit hyperactivity disorder, autism, and schizophrenia.

Recent research has identified differences in the brains of people with these disorders compared with those without. Despite the almost certain start of these conditions within the womb, they have remained impossible to diagnose until children begin to show clinical symptoms. If only researchers could spot the beginnings of these problems early in development, says Children’s National Health System researcher Catherine Limperopoulos, Ph.D., they might someday be able to develop interventions that could turn the fetal brain back toward a healthy developmental trajectory.

“Conventional tools like ultrasound and magnetic resonance imaging (MRI) can identify structural brain abnormalities connected to these problems, but by the time these differences become apparent, the damage already has been done,” Limperopoulos says. “Our goal is to be able to pick up very early deviations from normal in the high-risk pregnancy before an injury to the fetus might become permanent.”

Before scientists can recognize abnormal, she adds, they first need to understand what normal looks like.

In a new study published in Cerebral Cortex, Limperopoulos and colleagues begin to tackle this question through the largest MRI study of normal fetal brains in the second and third trimesters of pregnancy. While other studies have attempted to track normal fetal brain growth, that research has not involved nearly as many subjects and typically relied on data collected when fetuses were referred for MRIs for a suspected problem. When the suspected abnormality was ruled out by the scan, these “quasi-controls” were considered “normal” — even though they may be at risk for problems later in life, Limperopoulos explains.

By contrast, the study she led recruited 166 healthy pregnant women from nearby low-risk obstetrics practices. Each woman had an unremarkable singleton pregnancy and ended up having a normal full-term delivery, with no evidence of problems affecting either the mother or fetus over the course of 40 weeks.

At least one time between 18 and 39 gestational weeks, the fetuses carried by these women underwent an MRI scan of their brains. The research team developed complex algorithms to account for movement (since neither the mothers nor their fetuses were sedated during scans) and to convert the two-dimensional images into three dimensions. They used the information from these scans to measure the increasing volumes of the cerebellum, an area of the brain connected to motor control and known to mediate cognitive skills; as well as regions of the cerebrum, the bulk of the brain, that is pivotal for movement, sensory processing, olfaction, language, and learning and memory.

Their results in uncomplicated, full-term pregnancies show that over 21 weeks in the second half of pregnancy, the cerebellum undergoes an astounding 34-fold increase in size. In the cerebrum, the fetal white matter, which connects various brain regions, grows 22-fold. The cortical gray matter, key to many of cerebrum’s functions, grows 21-fold. And the deep subcortical structures (thalamus and basal ganglia), important for relaying sensory information and coordination of movement and behavior, grow 10-fold. Additional examination showed that the left hemisphere has a larger volume than the right hemisphere early in development, but sizes of the left and right brain halves were equal by birth.

By developing similar datasets on high-risk pregnancies or births—for example, those in which fetuses are diagnosed with a problem in utero, mothers experience a significant health problem during pregnancy, babies are born prematurely, or fetuses have a sibling diagnosed with a health problem with genetic risk, such as autism—Limperopoulos says that researchers might be able to spot differences during gestation and post-natal development that lead to conditions such as schizophrenia, attention deficit hyperactivity disorder and autism spectrum disorder.

Eventually, researchers may be able to develop fixes so that babies grow up without life-long developmental issues.

“Understanding ‘normal’ is really opening up opportunities for us to begin to precisely pinpoint when things start to veer off track,” Limperopolous says. “Once we do that, opportunities that have been inaccessible will start to present themselves.”

Using 3-D MRI for fetal brain imaging during high-risk pregnancies

3DMRI

What’s Known
The placenta plays an essential role in the growth of a healthy fetus and, among other critical tasks, it ferries in oxygen and nutrients. During pregnancies complicated by fetal growth restriction (FGR), the failing placenta cannot support the developing fetus adequately. FGR is a major cause of stillbirth and death, and newborns who do survive face numerous risks for multiple types of ailments throughout their lives. In fact, studies have shown that nutrient depravation during gestation can have lasting consequences that may manifest themselves years or decades later in life. These risks can also cross generations, affecting future pregnancies.

What’s New
A team of researchers applied an advanced imaging technique, three-dimensional (3-D) MRI, to study brain development in these high-risk pregnancies. They are the first to report regional, tissue-specific volume delays for the developing fetal brain in FGR-affected pregnancies. The team compared overall fetal brain volume as well as regional brain volumes for a control group of healthy young pregnant women with a group of young women whose pregnancies were complicated by FGR. While fetuses in both groups grew exponentially as pregnancies progressed, the researchers began to see dramatic differences when they compared the volumes of specific regions of the brain, including the cerebellum, which coordinates balance and smooth movement; the deep gray matter, which also is involved in complex functions, such as memory and emotion; and the white matter, which is made up of millions of nerve fibers that connect to neurons in different regions. Because there are no biomarkers to spot early brain failure, 3-D MRI imaging may fill this knowledge gap.

Questions for Future Research
Q: Certain regions of the brains of FGR-affected infants show accelerated volume. Are these differences regional or global?
Q: Is accelerated brain volume in FGR-affected infants a result of heightened stress that these fetuses experience in the womb?
Q: How do differences in regional brain volume relate to later neurodevelopmental impairment that some FGR-affected infants experience?

Source: “Impaired Global and Tissue-Specific Brain Development in the Growth-Restricted Fetus.N. Andescavage, J. Cruz, M. Metzler, A. du Plessis, and C. Limperopoulos. Presented during the 2016 Pediatric Academic Societies Annual Meeting, Baltimore, MD. May 2, 2016.