Di-butyl phthalate, a common ingredient in consumer and personal care products, including the coating on some pill formulations, may alter sperm RNAs, according to a discovery following more than a decade of collaboration between scientists at the Wayne State University School of Medicine in Detroit and the Harvard T.H. Chan School of Public Health in Boston.
Previous studies have already shown that phthalates are known endocrine disruptors suspected of affecting reproductive function. The endocrine system is a network of glands that produce and release hormones that help control body functions, including reproduction. Although considerable literature suggests that gestational and neonatal phthalate exposure is detrimental to reproductive function of the offspring, the health effects of phthalates on human male reproductive function is not fully understood.
The Mesalamine and Reproductive Health Study, or MARS, was designed to address the physiological effect of in vivo phthalate exposure on male reproduction in patients with inflammatory bowel disease, or IBD. The MARS study was designed to assess semen quality and hormone levels in human males through a novel cross-over and cross-back study after exposure to, and then removal of exposure to, very high-DBP found in the coatings of some medications used to treat IBD.
The Detroit team was led by Stephen Krawetz, Ph.D., associate director of the C.S. Mott Center for Human Growth and Development at Wayne State, and the Charlotte B. Failing Professor of Fetal Therapy and Diagnosis in the Department of Obstetrics and Gynecology and the Center for Molecular Medicine and Genetics.
Patients with IBD are often prescribed mesalamine, a medication which in some formulations contains DBP in the coating to allow for release of the active ingredient in the terminal small intestine and colon.
“If you ingest something in your gastrointestinal tract, what are the long-term ramifications of going to the reproductive organs?” Dr. Krawetz asked.
As part of the effort, the effect on sperm RNAs to di-butyl phthalate exposure was longitudinally assessed using the cross-over, cross-back design of high or background exposures to DBP. Each individual served as their own control. They found that their measurement – ribonucleic acid, present in all living cells – did not return to normal non-exposed levels after the 90 days.
“This suggests to us that the effects did not have a long enough time to clear. If you have an exposure and you can measure that exposure, how long can that last? And can you come back to a normal state?” he added.
In 2008, he teamed up with Russ Hauser, Ph.D., the Frederick Lee Hisaw Professor of Reproductive Physiology and chair of the Harvard T.H. Chan School of Public Department of Environment Health.
The article, “The effects of di-butyl phthalate exposure from medications on human sperm RNA among men,” born from the collaboration between Drs. Krawetz and Hauser, was published this week in Nature’s Scientific Reports.
“This is the result of all of those years of work. We’ve spent a long time working on the technology,” Dr. Krawetz said. “We’ve developed a series of assays based on RNA markers for sperm fitness to predict fertility, all toward the goal of a birth of a healthy child. This is in the framework of a father’s contribution. It’s not always up to the female. The male plays as integral of a part in the whole process. If you can monitor progression back to normal state, can there be optimal timing to conceive a child? Potential damage minimized? That’s what we’re working toward.”
The researchers found that as DBP levels were altered, numerous sperm RNA elements were differentially expressed, suggesting that exposure to, or removal from, high DBP produces effects that require longer than one spermatogenic cycle – equal to 72 days – to resolve. In comparison, small RNAs were minimally affected.
“While initial study medication implicated different biological pathways, initiation on the high-DBP condition activated oxidative stress and DNA damage pathways. The correlation of sperm RNA elements with specific genomic repeats suggests a regulatory role,” Dr. Krawetz said.
The researchers are also interested in studying the effects of longterm exposures in unknown environments, especially in members of the armed services, all with the goal of minimizing the effect of exposure on future generations.
The study team also included Molly Estill, Ph.D., a past graduate student in the Center for Molecular Medicine and Genetics. The work was part of her dissertation for which she was awarded her doctorate.
In Boston, Feiby Nassan, Sc.D., a postdoctoral fellow in the departments of Environmental Health and Nutrition at Harvard; and Alan Moss, M.D., an associate professor of Gastroenterology at Beth Israel Deaconess Medical Center in Boston, also collaborated and contributed.
The study was supported in part by the Charlotte B. Failing Professorship to Dr. Krawetz, and National Institutes of Health grants ES017285, ES009718 and ES000002 to Dr. Hauser.