Chemicals found in Chinese folk medicines may be used to make next generation of 'molecular condoms' that may serve as a safe alternative to today's hormone-based contraceptives, scientists say. The chemicals, extracted from two plants, thunder god vine and aloe, are effective at low doses and have no adverse effect on egg or sperm, other than preventing a key step in fertilisation - the meeting of egg and sperm. 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. According to researchers from the University of California (UC) Berkeley in the US, the chemicals may serve as an emergency contraceptive taken either before or after intercourse, or as a permanent contraceptive via a skin patch or vaginal ring. 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 fertilisation, they may be a more acceptable alternative in the eyes of those who object to emergency contraceptives that prevent the implantation of a potentially viable fertilised egg. These two plant compounds block fertilisation at very low concentrations - about 10 times lower than levels of levonorgestrel in emergency contraceptives, said Polina Lishko, an assistant professor at UC Berkeley. "They could be a new generation of emergency contraceptive we nicknamed 'molecular condoms,'" said Lishko, 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 fertilisation in the first place, it could potentially be a better option," she said. Purusing books on natural contraceptives used by indigenous peoples around the world, researchers came across several non-steroid chemicals isolated from anti-fertility plants. One of these was pristimerin, from the plant Tripterygium wilfordii, also known as "thunder god vine." Leaves from the plant have been used as an antifertility drug in Chinese traditional medicine, though some compounds in the leaves are poisonous. It has also been used as a folk remedy for rheumatoid arthritis. The other chemical was lupeol, which is found in plants such as mango and dandelion root.
While it has been tested as an anticancer agent, it was not suspected of having contraceptive properties. Researchers found that both pristimerin and lupeol prevented the sperm's power kick. "It doesn't kill sperm basal motility. It is not toxic to sperm cells; they still can move. But they cannot develop this powerful stroke, because this whole activation pathway is shut down," said Lishko. The research was published in the journal Proceedings of the National Academy of Sciences.
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