Folk contraceptives lead researchers to drugs that block fertilization
Two chemicals found in anti-fertility folk medicines block a key step in fertilization—the meeting of egg and sperm—and may make effective alternatives to today's hormone-based contraceptives, which sometimes cause side effects.
The chemicals are effective at low doses that seem to have no adverse effect on egg or sperm, other than to prevent the sperm from pushing through the cells that congregate around the egg and an enveloping membrane called the zona pelucida.
They work by stopping sperm's power kick, which is normally stimulated by the hormone progesterone secreted by cells surrounding the egg and makes the sperm's tail whip forcefully to propel it toward and into the egg.
The chemicals could serve as an emergency contraceptive taken either before or after intercourse, or as a permanent contraceptive via a skin patch or vaginal ring, say researchers at the University of California, Berkeley. Human sperm take about five to six hours to mature once they enter the female reproductive system, which is enough time for the drug to enter the system and block the kick.
Also, because the chemicals prevent fertilization, they may be a more acceptable alternative in the eyes of those who object to emergency contraceptives, such as Plan B, that prevent the implantation of a potentially viable fertilized egg.
"Because these two plant compounds block fertilization at very, very low concentrations—about 10 times lower than levels of levonorgestrel in Plan B—they could be a new generation of emergency contraceptive we nicknamed 'molecular condoms,'" said Polina Lishko, an assistant professor of molecular and cell biology, who led the team that discovered the anti-fertility properties of the two chemicals. "If one can use a plant-derived, non-toxic, non-hormonal compound in lesser concentration to prevent fertilization in the first place, it could potentially be a better option."
Lishko, first author Nadja Mannowetz, a project scientist, and former postdoctoral fellow Melissa Miller will report their findings online May 15 in the journal Proceedings of the National Academy of Sciences.
Hormones surrounding the egg trigger hyperactivation in sperm cells. The whip-like motion of the sperm's tail provides the power kick it needs to penetrate and fertilize the egg. Credit: UC Berkeley graphic by Carin Cain.
Compounds extracted from two plants, thunder god vine and aloe, prevent hyperactivation in sperm, the power kick necessary to fertilize the egg. The compounds are potential emergency contraceptives. Credit: Carin Cain, UC Berkeley
