Gene-blocking contraceptive on the cards

23 October, 2007

A contraceptive drug that helps avoid the side effects of hormonal birth control is on the cards.

Currently used Oral contraceptives can cause nausea, headaches, low sex drive and can raise slightly the risk of deep vein thrombosis (DVT) and strokes.

A conference of the American Society for Reproductive Medicine was told that the new technique, called ‘RNA interference’ (RNAi), could stop sperm entering the egg.

RNA interference is a way of “silencing a gene” to stop it working properly.

Researchers from Brigham and Women’s Hospital in Boston, the United States, have identified a gene called ZP3, which is active in eggs just before they are fertilized.

The ZP3 gene produces a protein which allows the sperm to bind to the surface of the egg. If this protein is not there, the egg cannot be fertilized.

The Brigham and Women’s Hospital research team claimed that it “silenced” the ZP3 gene in mice, and found that they could not get pregnant.

Dr Zev Williams, who presented the research finding at the conference of the American Society for Reproductive Medicine, said: “We simply don’t have a contraceptive drug that is non-hormonal and reversible. What we are trying to do is to think about contraception in a new way. Obviously, there are going to be hurdles and it is going to take a lot of time, but the need is there and we think it can be achieved.”

Professor Bill Ledger, from the University of Sheffield, the United Kingdom, said a lot of women still had side effects, even on the modern hormonal contraceptives.

The Boston researchers estimate that it will be at least 10 years before clinical trials of an ‘RNA interference’ contraceptive would be made possible.

Dr Martin Fabani, a researcher in the technique at Cambridge University, the United Kingdom, said that obstacles would need to be overcome, and that there was no guarantee that side effects could be avoided completely. The therapy could have unwanted effects elsewhere in the body.

The research into the ZP3 gene, Dr Martin Fabani added, has one advantage in this respect, as the gene appears to be active only in eggs prior to the moment of fertilization, and nowhere else in the body. This means that it could be “switched off” without necessarily affecting either the prior development of the egg and ovulation, or other parts of the body.