HERSHEY, Pa. — Many urban and suburban areas have high levels of ground-level ozone, an air pollutant that can adversely affect lung and heart health. New research in mice suggests that breathing high levels of ozone could also affect women’s ability to conceive.
Dr. Carla R. Caruso, a resident physician at the Hershey Medical Center, recently presented this research, which was led by Patricia Silveyra, assistant professor of pediatrics at Penn State College of Medicine, at the American Society for Investigative Pathology’s Experimental Biology 2015 meeting.
In some areas, ozone can reach high levels in the summer because the bright sunlight and heat combine with compounds from industrial emissions, car exhaust, and gasoline vapors to form the air pollutant.
“It is important that we know what is in the air we breathe and understand how it can affect our health,” said Silveyra. “We don’t know a lot about the damaging effects of ozone, but since it does increase inflammation in the lungs, it is possible that this inflammation could affect more than one system in the human body.”
Silveyra and her team were studying sex differences in the effects of ozone on lung inflammation in mice when they discovered that short exposures to ozone affected female levels of progesterone, a major reproductive hormone involved in ovulation and pregnancy. To examine this further, they designed an experiment in which female mice were exposed to two parts per million (ppm) of ozone for 3 hours on the day the mice were expected to ovulate. Other studies have shown that this level of exposure in mice is roughly analogous to a person breathing high levels of ozone in a city.
“We found that breathing ozone on the day of ovulation not only decreased progesterone levels in female mice, but also reduced the number of ovulated eggs,” said Caruso. “In addition, this acute exposure to ozone affected important brain and ovarian signaling events that are key for the ovulation process.”
The levels of progesterone in the blood of female mice on the day of ovulation decreased from a normal value of 8 nanograms per milliliter (ng/ml) in females breathing filtered air, to an average of 2 ng/ml in mice breathing ozone. When the investigators compared the number of ovulated eggs the following morning, they found a statistically significant reduction of 30 percent in females exposed to ozone. Expression of key enzymes involved in the progesterone synthesis pathway was also significantly reduced in the ovaries of ozone-exposed female mice.
Based on their findings, the researchers postulate that women in large cities could experience fertility issues from inhaling high concentrations of ground-level ozone. However, they caution that their findings are preliminary and that the research involved only mice, not people.
“Population studies evaluating fertility complications in geographical areas with high- and low-ozone pollution levels, as well as clinical studies conducted in women of reproductive age can help elucidate these concerns,” Silveyra said.
The researchers are now working to understand the mechanisms of ozone’s effects on ovulation in mice.
The study was funded by grants from the National Institutes of Health (K12HD055882 and R25HL103166).