Using technology borrowed from the National Aeronautics and Space Administration (NASA), scientists at the University of Pittsburgh's McGowan Institute for Regenerative Medicine have taken the first steps toward successfully preserving ovarian tissue from rats and mice in culture, including immature egg follicles, according to a study in the current issue of the journal Tissue Engineering.
Such techniques may prove to be valuable in protecting the fertility of a woman with cancer whose future childbearing potential is threatened by the very chemotherapy or radiation treatments necessary to save her life.
"While it is possible for ovaries to be removed and frozen before cancer treatment, there is currently no reliable way to generate mature eggs once the stored tissue is thawed," said Alan J. Russell, Ph.D., director of the McGowan Institute and senior author of the study. "Finding a safe, dependable way to produce healthy eggs from preserved ovaries will be a significant advance toward conserving fertility for cancer patients."
In the most recent study using ovarian tissue in rats and mice, University of Pittsburgh scientists focused their efforts on ovarian tissue structures, including immature eggs and follicles, the main functional portion of the ovary. Under normal circumstances, follicles remain dormant until triggered at puberty to cycle through several stages of development before reaching full maturity. Eggs are nurtured within the follicle. Once all the follicles are gone, ovaries fail and a woman enters menopause.
"We looked at using suspension culture systems to provide a uniform setting for follicles that is similar to the natural ovarian environment," said Dr. Russell, who also is professor of surgery at the University of Pittsburgh School of Medicine.
Custom-designed rotating wall vessels and orbiting test tubes were the suspension systems used, explained Elizabeth McGee, M.D., a study co-author who is assistant professor of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh School of Medicine and a McGowan Institute faculty member.
"Test tubes are housed in an orbiting device designed to gently agitate a special growth medium just enough to prevent follicles from settling on the surface – to keep them surrounded by fluid," added Dr. McGee, who also is an assistant investigator at Pittsburgh's Magee-Womens Research Institute. "Ovarian follicles are highly fragile. We wanted to eliminate as much opportunity for mechanical damage as possible."
For comparison purposes, some ovarian tissue was encapsulated in a special protective polymer gel and some was not, Dr. McGee said. Culture wells, test tubes and rotating wall vessels were incubated for 72 hours, and follicle diameters were measured daily. Between 25 and 60 follicles were analyzed for each treatment group.
In addition, follicles were cultured in the presence and absence of follicle-stimulating hormone (FSH) in the specially designed systems and in a conventional culture system to evaluate resulting changes in egg structure and maturation using the different mediums and culture systems.
"Our goal is to understand which features of the artificial environment contribute significantly to egg cell changes," said Dr. Russell.
At the end of the 72-hour culture period, follicles were evaluated for changes in shape and levels of development. There were vastly different rates of growth depending on culture conditions. Follicles cultured in a growth medium that included FSH using the NASA-inspired techniques developed larger diameters, growing at roughly double the rate of those in conventional culture, the authors report. In addition, these follicles were more likely to maintain their normal spherical shape than those supported in other ways.
"This study is the first to look at this new environment for the culture of immature rat and mouse follicles," said Dr. Russell. "We found that a suspension culture in combination with micro-encapsulation does a better job of promoting follicular growth than more conventional methods."
"More studies are needed to evaluate these techniques in the longer term as well as to discover optimum conditions for follicle growth," Dr. Russell said. "Still, the results represent a promising step in the right direction."