Findings correlate with clinical observations of more fetal abnormalities and other Zika-related health problems in late versus early pregnancy

Tampa, FL (Feb. 2, 2021) — A preclinical study by a University of South Florida Health (USF Health) Morsani College of Medicine research team has discovered a new mechanism for how Zika virus passes from mothers to their children during pregnancy – a process known as vertical transmission.

The researchers showed, for the first time, that specialized cells lining the uterus (maternal decidual cells) act as reservoirs for trimester-dependent transmission of the virus through the placenta – accounting for both the fetus’s greater susceptibility to first-trimester Zika infection and for the more serious congenital defects observed in early versus late pregnancy. They also report that the agent tizoxanide inhibits ZIKA virus in maternal decidual cells grown in the lab, offering promise for preventing perinatal transmission that can cause devastating malformations and brain damage in developing fetuses and infants.

The findings appeared Dec. 1, 2020 in the Journal of Immunology.

The study was led by co-principal investigators Ozlem Guzeloglu-Kayisli, PhD, a USF Health associate professor of obstetrics and gynecology, and Charles J. Lockwood, MD, USF Health senior vice president, dean of the Morsani College of Medicine, and a professor of obstetrics and gynecology specializing in maternal-fetal medicine.

“If we can better understand Zika virus vertical transmission and successfully block infection in maternal (decidual) cells early in the pregnancy, the virus will not pass through the placenta to reach the fetus and it is less likely to cause severe abnormalities,” said Dr. Guzeloglu-Kayisli, the paper’s lead author.

Ozlem Guzeloglu-Kayisli, PhD, USF Health associate professor of obstetrics and gynecology, was the paper’s lead author.| Photo by Allison Long, USF Health Communications and Marketing

Charles J. Lockwood, MD, dean of the USF Health Morsani College of Medicine and a professor of obstetrics and gynecology specializing in maternal-fetal medicine, was a co-principal investigator for the Zika study along with Dr. Guzeloglu-Kayisli. | Photo by Freddie Coleman, USF Health Communications and Marketing

The widespread global alarm caused by the spread of mosquito-borne Zika virus throughout the Americas in 2015-2016 dissipated after the virus all but disappeared in 2017. Yet, resurgence remains possible in areas where the Aedes aegypti mosquito is prevalent, and there is no treatment or vaccine available for Zika virus infection.

While most Zika-infected adults show no symptoms, the virus can cause minor flu-like symptoms, and in rare cases has been associated with Guillain-Barre syndrome. However, Zika poses the most concern for pregnant women, because up to one in 10 newborns of affected mothers suffer Zika-associated birth defects, including smaller than normal head size (microcephaly) that can lead to developmental disabilities and other health problems. Zika has also been linked to pregnancy complications, including preterm birth, preeclampsia and miscarriage. Moreover, timing appears important. Mothers infected in the first trimester are much more likely to have babies with severe Zika birth defects than mothers infected in the third semester.

The placenta, the organ supplying maternal oxygen and nutrients to the growing fetus, has ways to prevent most pathogens, including viruses, from crossing its protective maternal-fetal barrier. A subtype of fetally-derived placental cells known as syncytiotrophoblasts, in direct contact with maternal blood, are assumed to be the site where the Zika virus enters the placenta, leading to potential fetal infection. However, Dr. Ozlem Guzeloglu-Kayisli said, these particular trophoblasts resist Zika virus attachment and replication.

Above and close-up below: A model for mother-to-fetus transmission of Zika virus (green particles) through maternal decidual cell-mediated infection of villi attaching the placenta to the endometrium (uterine lining). | Images courtesy of USF Health first appeared in the Journal of Immunology: doi: 10.4049/jimmunol.2000713

To learn more about how Zika gets through the placental wall, the USF Health team began by investigating the cellular and molecular mediators of Zika virus replication. Among their key findings, the researchers:

–  Showed that specialized uterine cells from both pregnant and nonpregnant women were highly infectable by Zika virus. These immunologically active decidual cells, which line the uterus in preparation for and during pregnancy, form the maternal part of the placenta closest to the fetus.

–  Identified a more than 10,000-fold higher expression of the Zika virus attachment-entry receptor in the maternal decidual cells than in the fetal trophoblasts. Once inside the maternal cells, the Zika virus (an RNA virus) hijacks the cellular machinery to make proteins needed to copy its genetic material and churn out new viral particles. The proliferation of viral particles released from the maternal cells are then transmitted through branch-like vascular projections (villi) on the placenta’s surface layer where they can infect fetal trophoblast cells otherwise resistant to Zika virus.

–  Found that the efficiency of viral replication was significantly greater in first-trimester decidual cells than in those from term pregnancies.

–  Concluded that maternal (decidual) cells likely serve as the source for initial Zika virus infection and enhance subsequent transmission through the placenta to the fetus. “Moreover, trimester-dependent responses of decidual cells to Zika virus help to explain why pregnant women are susceptible to Zika infection and why the subsequent effects are more detrimental in the first trimester than in late pregnancy,” the study authors wrote.

–  Demonstrated that tizoxanide, the active metabolite of FDA-approved antiparasitic drug nitazoxanide, effectively impeded Zika virus infection in both maternal decidual cells and fetal trophoblast cells. The drug has been shown preclinically to inhibit a broad range of flu-like viruses and is being tested clinically against coronavirus. The finding warrants further testing of tizoxanide to block perinatal transmission of Zika virus and thereby protect the fetus from harmful outcomes, the researchers conclude.

The team’s work was supported in part by a Zika Research Initiative grant from the Florida Department of Health.

High levels of fine particulate air pollutants are associated with several select congenital heart defects and the highest level of benzene links to increased prevalence of orofacial clefts, a new USF College of Public Health study found. The clinical significance of the environmental factors in the risk for birth defects requires more study, however, because several defects showed no link to these pollutants.

The COPH USF researchers used data from the Florida Birth Defects Registry and air pollution monitoring data from the U.S. Environmental Protection Agency (EPA) Air Quality System to examine how maternal exposure to air pollutants benzene and PM_2.5 affects the risk of birth defects. Their study, “Associations between exposure to ambient benzene and PM_2.5 during pregnancy and the risk of selected birth defects in offspring,” was published in the July issue of Environmental Research.

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“Pollution is very common and at this point there isn’t a lot of knowledge on what causes birth defects,” Jean Paul Tanner, epidemiologist and statistical data analyst of the USF Birth Defects Surveillance Program, said. “We have to try and dig deep and see what some of the causes are; while we did find some associations, it’s something that needs to be looked at further.”

Tanner and principal investigator Dr. Russell Kirby of the USF Birth Defects Surveillance Program worked with worked with Dr. Amy Stuart, associate professor in the COPH Department of Environmental and Occupational Health, to examine how maternal exposure to air pollutants benzene and PM_2.5 impacted risk of birth defects.

Drs. Haofei Yu and Jason Salemi, alumni of the COPH, also contributed to the study.

Individuals regularly come into contact with PM_2.5, short for particulate matter less than 2.5 microns in diameter. It is a combination of particles suspended in air from pollution emitting agents such as cars, power plants, factories and natural sources, such as forest fires.

“PM_2.5 is a common pollutant or criteria pollutant. It’s regulated with a level in air that is considered a maximum allowable level and those are called national ambient air quality standards,” Stuart said. “It is the number one pollutant from a health impact standpoint.”

Benzene is less common but also important to health, according to Stuart.

“Benzene is a hazardous air pollutant and it is specifically known to be substantially present in urban areas,” Stuart said. “It comes from off gassing of gasoline, and other sources, including chemical manufacturing; it is one of approximately 190 listed hazardous air pollutants the EPA lists, and of that list, it’s one of the 30 that the EPA is most concerned with in urban areas.”

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The researchers obtained data from the Florida Birth Defects Registry for births taking place from 2000 to 2009 and involved critical congenital heart defects, orofacial clefts and spina bifida.

They then estimated pollutant levels affecting each birth using data from the EPA’s ambient air quality records and addresses listed on the birth certificates, to gauge the mother’s exposure to PM_2.5 and benzene during pregnancy.

Results of the study indicate that higher levels of ambient PM_2.5 exposure are associated with several birth defects. The highest benzene exposure level was found to be associated with increased prevalence of orofacial clefts, but also with decreased prevalence of one heart defect. However, substantial uncertainty remains regarding whether these links are clinically important because no association was found for several related defects.

“There is a lot we still don’t know and I would very much like us to get the point where there is quite a lot more that we do know,” Kirby said. “There is a thought that environmental factors play a major role in birth defects in not only directly influencing, but also possibly interacting with genes, but we don’t really know very much about it. If we were to find an association between exposure to some pollutant early in pregnancy and birth defects, we would need to do more advanced studies to see what the nature of the association is.”

Data from the study may be obtained by contacting Dr. Kirby at rkirby@health.usf.edu.

Article citation:
Tanner, J.P., Salemi, J.L., Stuart, A.L., Yu, H., Jordan, M.M., Duclos, C., Cavicchia P., Correia, J.A., Watkins, S.M., & Kirby, R.S. (2015). Associations between exposure to ambient benzene and PM_2.5 during pregnancy and the risk of selected birth defects in offspring. Environmental Research, 142, 345-353.

Story by Anna Mayor, College of Public Health