Nitric oxide could one day help women in their 30s and 40s remain fertile longer

Researchers have found that an important chemical compound, nitric oxide, appears to slow or reverse the aging of eggs in mouse ovaries. The finding suggests nitric oxide could one day help women in their 30s and 40s remain fertile longer and increase their chances of having healthy babies, the scientists say.

The finding, by investigators at Wayne State University School of Medicine in Detroit, was published in the Aug. 30 issue of the American Chemical Society's journal Biochemistry.

In their laboratory study, Anuradha Goud and colleagues gathered more than 1,500 eggs from mouse ovarian ducts one to two hours or four to six hours after ovulation. Mouse eggs that aren’t fertilized within hours of ovulation begin to age rapidly. After about six hours, these eggs are less likely to be fertilized properly, leading to chromosomal abnormalities in the embryos.

To prevent this, the researchers exposed the eggs to varying concentrations of nitric oxide, a multipurpose signaling molecule that, among other things, helps keep arteries supple and helps men achieve erections. In the "older" eggs, the compound appeared to slow the hardening of the eggs’ outer shells, diminish the activity of ooplasmic microtubules (the structures that attach to chromosomes and guide them to different parts of a cell during division), increase the release of cortical granules (the molecules responsible for preventing egg fertilization by more than one sperm) and delay other signs of aging.

In addition to possibly extending fertility in women, the results suggest that nitric oxide could help prevent chromosome errors during early embryonic development. These errors can lead to Down syndrome, spontaneous miscarriages and other problems associated with pregnancies later in life.

"Eggs from older women may be particularly sensitive to aging after they are released from the ovaries," said Husam Abu-Soud, Ph.D., a Wayne State University researcher and co-author of the study. "As a result, the time available for optimal fertilization of these women’s eggs may be quite a bit shorter than the time frame in younger women." But exposing the eggs to appropriate levels of nitric oxide "could extend this fertilizable time window in both old and young women," he speculates. The results also raise the possibility that nitric oxide could be used to enhance the fertility of eggs harvested for use during in vitro fertilization.

Although it is unclear how nitric oxide produced these results, the researchers theorize that the compound may prevent irregularities in calcium release within the eggs. These irregularities have been linked to aging of mammalian eggs.

The American Chemical Society is a nonprofit organization, chartered by the U.S. Congress, with a multidisciplinary membership of more than 158,000 chemists and chemical engineers. It publishes numerous scientific journals and databases, convenes major research conferences and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.