For humans, a drug made from a plant compound that has anti-inflammatory properties represents a possibility for prenatal treatments that are personalized to meet the needs and metabolisms of individual babies.
In humans, Down Syndrome is also called Trisomy 21 — with “trisomy” meaning a third instance of any paired chromosome, and “21” referring specifically to the human chromosome number 21 (of 46). Quite literally, all of the neurological, muscular, cardiac, dental, endocrine, gastrointestinal, sensory, oncological, and fertility symptoms that can manifest with Down Syndrome are caused by the extra chromosome 21 in the genetic makeup of a baby.
Not all of these physiological systems are disordered in everyone with Down, though common to the syndrome is some degree of developmental delay and intellectual disability. Historically, treatments in humans have had disappointing results, perhaps because most have been applied during the late teen years or during adulthood.
As Diana Bianchi, Director of the National Institute of Child Health and Human Development and a senior researcher at the National Human Genome Research Institute, explained in a phone call, “The brains of teens and adults may be less flexible (and therefore potentially less responsive to interventions) than the brains of fetuses. Amniocentesis and other prenatal screenings that reveal fairly early in a pregnancy if a fetus has Trisomy 21 are almost universally available to women in the United States. This presents an opportunity; before birth may be the ideal time to try to intervene.”
Bianchi acknowledged that medical interventions on fetuses are fraught with ethical complications because of the potential for further damaging a baby before it is even born. “Safety, she said, “is paramount.”
Bianchi is senior author of a paper published today in the American Journal of Human Genetics. It details a trial conducted on mice that were bred to have Down Syndrome characteristics. The trial is of the prenatal use of apigenin, a plant compound found in chamomile, celery, parsley, peppermint, and citrus fruits.
According to Bianchi, prenatal imaging studies of human fetuses with Down Syndrome show neurological abnormalities. Typically with Down, over the course of a pregnancy production of new brain cells is slowed, as is production of the nerve fibers connecting the cells, the myelin (or cellular insulation) that protects nerve fibers, and the synapses that permit nerve cells to pass electrical and chemical signals to each other.
The evidence of these early impairments suggests that Down Syndrome is not a neurodegenerative disorder but a developmental one.
Suspecting that inflammation during brain development might be to blame, Bianchi and her team of investigators set out to address neurological inflammation in mice fetuses. Mice have a vastly different genome from humans. In mice the rough equivalent of Down doesn’t result from a trisomy of chromosome 21. The mice model used in Bianchi’s trial (it is called Ts1Cje), represents a partial triplication of the mouse chromosome numbered MMU16.
Bianchi’s team hopes that, within several years, they can run trials of treatments for human fetuses. Because of this, in their mouse trial they took extra care to do no harm to the Ts1Cje mice. Additionally, they were diligent about creating an intervention that could be delivered humanely to mouse mothers. They knew that any medicine or compound they used would need to infuse into fetuses from placenta. It would also need to cross the fetus’ blood-brain barrier, which is the cellular layer that protects the brain by allowing only certain substances to cross into it.
Bianchi’s team used publicly available software to help them select apigenin from a range of nine possible compounds. “We had no intention of limiting ourselves to a natural substance approach,” Bianchi explained. “Our goal was simply to find a compound that had genetic markers that met all of our chemical and functional criteria. The software identified for us which of the nine compounds to use in our trail.”
Bianchi did note in the call that, in other studies, apigenin has been shown to have anti-inflammatory properties.
The research team incorporated apigenin into the chow of the pregnant and nursing Ts1Cje mothers. They later fed it to the weaned Ts1Cje pups. The mice that were given apigenin scored better in tests of spatial and olfactory memory than did control-group mice. The team also found that apigenin-treated mice had benefitted from more blood vessel and nervous system growth and that they had less inflammation overall.
Importantly, apigenin appeared to do no harm. The investigators found no significant increase in birth defects or deaths among Ts1Cje pups treated prenatally and postnatally with apigenin.
According to Bianchi, the trial depicted in today’s issue of The American Journal of Human Genetics was a proof-of-principle trial for an approach that ultimately could provide interventions that are personalized for individual human fetuses. To explore this possibility, the researchers tested the effect of apigenin on cells sloughed off by human fetuses and harvested during routine amniocentesis. They found that, in the lab, apigenin had anti-inflammatory effects on those cells.
Bianchi says that, ultimately, she hopes to identify several compounds that can work safely and effectively to calm inflammation in human Down Syndrome fetuses. “Not everyone metabolizes any given drug or food in the same way,” she pointed out in the phone interview. “Ideally we can eventually know of several compounds that have a moderating effect on Down. We can test each one on sloughed-off cells gathered during routine prenatal screening, and then select the single approach most appropriate for any given fetus.”
A lot of preclinical work remains to be done, even with apigenin, before that scenario can become a reality. Bianchi specified that she and her researchers still want to test different doses of apigenin. They want to identify any measures in which mouse fetuses treated with apigenin do more poorly than fetuses who aren’t treated. They want to supplement their work with the Ts1Cje mice with trials conducted on other models of Down Syndrome in mice. They want to determine if apigenin or some metabolite or component of it is responsible for its anti-inflammatory effect.
“We also need to better understand why, in some measures in this early proof-of-principle trial, males treated with apigenin fared better than females and why, on other measures, females fared better than males. That difference was a surprise to us. Trying as we are to develop safe, personalized medicines, we need to know what that means.”
When asked how realistic the idea of treatments for human fetuses is, Bianchi was firm about the possibility. “The fact that virtually all pregnant women who get prenatal care in the United States are offered prenatal screening presents a huge opportunity. We are still nowhere near ready for a clinical trial with humans. But our goal is to help bring children into the world with the best capacity they can have. Our success in identifying the beneficial effects of apigenin in Ts1Cje mice is an incremental but significant step toward that goal.”