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Scanning electron microscope photos of human placental cells in an artificial
growth medium, a fibrous-bed bioreactor. The cells cling to polyester fibers. Photos
courtesy of the Laboratory of Perinatal Medicine, Department of Obstetrics and Gynecology,
Ohio State University. Full size images available through contact |
This represents a critical first step toward finding a way to test the safety of drugs that a woman can take during pregnancy without harming her fetus.
The cells provide scientists with the means to observe what happens to drugs that pass through a healthy placenta, not excised placental tumors or aborted placental tissue which are normally used in the laboratory.
Douglas Kniss, associate professor of obstetrics and gynecology at Ohio State, and Teng Ma, a graduate student in chemical engineering, grew the placental cells artificially using a new technique developed in cooperation with Shang-Tian Yang, professor of chemical engineering.
“The placenta is very important for the health of the
fetus, but little has been done to study the placenta in a dynamic
way -- a way close to conditions that actually exist inside the
body,” said Ma.
The researchers grew the cells in a bioreactor, a container stuffed with a matrix of polyester fibers. Unlike the alternative -- a flat surface such as a petri dish -- the bioreactor allows cells to grow and reproduce as they do in the body, clinging to the polyester fibers as they normally would to strands of human proteins. Liquid nutrients course steadily through the bioreactor, mimicking blood flow.
As a result, the placental cells not only survive in the bioreactor, they function as they do in the womb. Ma presented this research last month at the 216th national meeting of the American Chemical Society in Boston.
“Our objective is to use the cells in the bioreactor as an artificial placenta to test drugs,” said Ma. “Then we can avoid testing on humans or animals, both of which involve high costs and ethical problems.”
“To date, researchers have been using placental tumors -- which grow very well -- but they are obviously malignant, so they’re not very normal. The other option is to use abortion material, but there are ethical concerns about that, and more recently, legal concerns, so we avoided that altogether,” said Kniss.
Kniss and Ma decided to grow only trophoblast cells, the placental cells responsible for transferring nutrients from the mother to the fetus.
“I want to make sure that everyone understands that we are not attempting to grow organisms outside of the womb,” said Kniss. “We are attempting to develop models by which we can understand placental functions better, as well as provide the pharmaceutical industry with the means to assess the use of drugs during pregnancy.”
This work may aid the development of drugs that treat complications of pregnancy, such as infections, hypertension, seizure disorders, and metabolic diseases. It may also pave the way for treating fetal disorders chemically in the womb.
For this project, Kniss gathered an initial batch of trophoblast cells in 1989 from a patient at Ohio State University Hospital who underwent genetic testing to assure the health of her fetus during the first trimester of pregnancy. Such testing is routine for women like this patient who become pregnant in their 30s. The test showed that the fetus was healthy, and the woman went on to deliver a healthy baby with no complications.
Kniss froze some of the woman’s trophoblast cells. Periodically, he and Ma thaw a few cells and seed them in the bioreactor. This is the first time such experiments have been done with cells that are both normal and not obtained from abortion material.
The researchers have been able to maintain healthy trophoblast cells in the bioreactor for as long as four weeks.
“That’s the real crux of the project,” said Kniss. “Nobody else has been able to keep placental cells alive for more than one week. So our ability to grow them over long periods of time allows us to look at the long-term effects of drugs on the cell. What we’re ultimately trying to do is push the envelope further and grow cells for three or four months.”
Kniss added that the cells may live even longer than four weeks. Since he and Ma stopped the experiment to study the cells, they aren’t certain how long the cells will continue to grow if left alone.
Not only did the trophoblast cells reproduce in the bioreactor, but they became fully functional. The cells sprouted villi, the tree-like projections with which they absorb materials from the placenta.
Kniss said that a healthy placental cell grows villi because the projections increase the surface area of the cell and boost the amount of nutrients the cell can absorb and transport over a thousand fold.“The placenta is a very space-efficient organ,” said Kniss. “If you were to stretch one out, you could cover a surface about the size of a tennis court.”
Unlike flat cells grown on a plastic culture dish, the trophoblast cells in the bioreactor grow rounded and plump and arrange themselves in clusters as they would in the body. This allowed the researchers to test the normal functioning of the cells under various conditions.
At the American Chemical Society meeting, Ma discussed the latest finding of the project -- that the trophoblast cells reproduce very quickly when the researchers restrict the amount of oxygen in the bioreactor.
Kniss said that makes sense, since during the first few weeks of pregnancy, as an embryo travels down the mother’s fallopian tube to the uterus, it acquires very little oxygen. Yet this is the time that the cells proliferate the fastest. When the embryo attaches itself to the uterus and the umbilical cord forms, the embryo is bathed in oxygen, and cells put less energy into fast reproduction in order to assume specialized functions.
Kniss added that since he and Ma were able to maintain live trophoblast cells under low oxygen conditions for three weeks, this provides evidence that the cells are functioning normally.
Once they discover the best conditions for growing the cells, the researchers will begin exposing the trophoblast cells to drugs to see exactly what happens when a human placenta is exposed to them.
“Ultimately, we want the cells to react as they normally would in the body,” said Kniss. “We obviously can’t do human studies with these drugs, so we want something that is as close to the human condition as possible, but is still artificial.”
The National Institute of General Medical Sciences (NIGMS) is funding this research with a grant from its “Exploratory Studies for High Risk/High Impact Research” program. NIGMS is a component of the National Institutes of Health that supports basic biomedical research.