Polychlorinated biphenyls, better known as PCBs, are man-made industrial chemicals produced for over five decades in the U.S. and used in insulating fluids in transformers and electrical equipment along with plasticizers in paint and construction materials. Despite the worldwide ban on the production of PCBs in 1979, they remain an environmental problem because of their high persistence and leakage from existing applications and improper disposal. In the environment, researchers believe that they induce toxicity by disrupting the hormonal balance in humans and animals.
Chinedu Ahuchaogu, a December graduate with a master’s degree in toxicology, presented his thesis, “Cytotoxicity of Polychlorinated Biphenyl Congeners in Human Placental Trophoblast Cells,” early last month.
“Due to their persistent nature,” Ahuchaogu said, “PCBs are transferred from mothers to the fetus across the placenta, or to nursing infants and babies via breast milk, which may lead to developmental and neurological problems from repeated exposure to low levels of PCBs.”
Each PCB has a common structure of a biphenyl molecule with one to 10 chlorine atoms attached; each possible variant is called a congener. Ahuchaogu’s research focused on “how two different congeners of PCBs (PCB 152 and 118) affect the normal growth of human placental cells in the presence and absence of estrogen hormone.” Studies have shown, he said, that estrogen influences various aspects of placental function and fetal development in both humans and animals.
“We also examined the effect of PCB 153 on estrogen receptor transcription factor, a protein that controls the rate of transcription of genetic information from DNA to messenger RNA by binding to a specific DNA sequence,” he said.
The results of his research demonstrated that exposure of the placental cells to PCB congeners reduced cell viability and growth as the PCB concentrations increased.
“Exposure of the placental cells to environmentally relevant concentrations of PCB 153 and PCB 118 resulted in significant reduction in estrogen-induced cell viability and growth,” Ahuchaogu said. “The action of PCB 153 or PCB 118 in placenta cells was blocked by estrogen receptor antagonists, ICI 182, 780, PHTPP and estrogen receptor modulator, tamoxifen, which indicates that the toxic effect is mediated through estrogen receptors involved in cell viability and growth.”
It was also discovered, he said, that PCB 153 antagonized the estrogen-receptor activation in a concentration dependent manner. “In summary, our results showed that the human placenta is a target of PCB toxicity, and current environmental PCB exposure levels are a risk to reproductive health.”
“PCB 118 and PCB 153 are of great concern since they are highly accumulated and frequently detected in human tissues. Because PCBs are a potential health hazard, understanding the risk factors associated with individual PCBs is important particularly in vulnerable populations, such as pregnant women, fetuses, infants and children,” said Dr. Ahmed Elnabawi, an associate professor of toxicology in UMES’ Department of Natural Sciences and Ahuchaogu’s research adviser. “Our results have public health implications for infant health, and potentially later adult health. The results highlight approaches that could shed light on the possible associations between environmental chemicals that act on the endocrine system and compromised normal growth and developmental outcomes. In addition, our results could explain how environmental toxicants may trigger underlying biological mechanisms.”
Ahuchaogu is a native of Abia, Nigeria. He received a bachelor’s in environmental management and toxicology from the Federal University of Agriculture Abeokuta in his home country.
While at UMES, he was a graduate teaching assistant in the Department of Natural Sciences and looks “forward to an opportunity to become a mentor for others like me within the field.”
Gail Stephens, agricultural communications and media associate, School of Agricultural & Natural Sciences, 410-621-3850, gcstephens@umes.edu.
