Cocktail inspires male contraceptive

A reversible contraceptive technique for males has been developed by researchers in China.
02 February 2019

Interview with 

Bill Colledge, University of Cambridge


Sperm surrounding an egg cell.


A reversible contraceptive technique for males has been developed by researchers in China. So far it’s been tested only in rats, but appeared to be safe. The approach involves injecting into the vas deferens - the tubes that connect the testes to the inside of the body - a small amount of a thick, gel-like substance that blocks the movement of sperm. Injected in a series of layers above this is a solution of gold nanoparticles that can absorb infrared or heat energy, and a chemical that can dissolve the gel plug and reverse the blockage. The idea is that focal heat applied to the area is absorbed by the nanoparticles; this releases the gel-dissolving chemical, which then unblocks the vas deferens. Bill Colledge is a reproduction specialist at Cambridge University’s Physiology Department. He wasn’t involved in the study but agreed to take Chris Smith through the paper describing the work…

Bill - This group are trying to develop a novel method for male contraception because at the moment there are very few opportunities for male contraception, other than using a condom or having a vasectomy. And what they decided that they would try and do is to block the tube - or the duct - that allows the sperm to get out of the testes and out of the body.

Chris - And is that reversible so you could do this for a period of time and then turn the effect off?

Bill - Yes it is. I mean that's one of the novelty of the technique is that it should be reversible. There are other groups that are trying to do a similar approach of blocking the duct, but those are generally irreversible. And this approach that they have developed is incredibly novel in that they believe that, by a simple heat treatment, they would be able to reverse it.

Chris - Talk us through how it works; what's the technique?

Bill - What the group have done, and they've tested this in rats, is they have put substances into the duct that the sperm have to move through; and these substances are in several layers, and one of the substances is a sort of thick compartment that will prevent the sperm from moving. The other substances, when activated by heat, can become liquid and then they can dissolve the compartment that's blocking the sperm, so it's therefore reversible.

Chris - So it's a bit like a "tequila sunrise" then, in the sense you've got these layers: you've got a thick layer that provides the blockade, but then you've got higher layers that are capable of dissolving the blockade but only when they get near it but they're not near it to start with, unless you put some heat in there?

Bill - Absolutely it is just like a cocktail! In fact the people in the paper say that they were inspired by looking at a cocktail with different layers...

Chris - It's ironic that they're talking about cocktails in a paper about a sort of chemical vasectomy!

Bill - Well it is indeed! Yes! But I think it's a it's a very very novel and innovative approach. It needs to be developed; it needs to be progressed to see whether it would work in humans - they've only just tested it in rats, and they've monitored the fertility of the rats after this treatment for a period of 65 days or so. We don't know whether it can last longer than that. And that's clearly going to be important in translating it into the clinic, because you don't want to have to keep having this treatment. You want it to last for a fairly long time.

Chris - In terms of actually how the heat reversibility bit works, how have they done that?

Bill - The different layers have different chemical components and to reverse the blockage what they do is they heat the testes, with just a infrared heat source, and that liquefies one of the layers, which then releases the chemical in a different layer, which will then liquefy the blockage to allow the sperm to progress.

Chris - Does this mean though that if I go and take a hot bath I could accidentally dissolve this? I mean, how hot do you have to make the tissue, because I can't see many people jumping at the chance to have their testicles irradiated with infrared sources in order to reverse this. It might not be comfortable!

Bill - That's an absolutely perfect point and it was one of the issues that when I read the paper came to mind. They are heating the tissue up to about 42 and a half degrees Celsius, which isn't that hot - and certainly one can have a hotter bath than that - so I was concerned that it is possible that you have a hot bath and you inadvertently become fertile again. I think what they can possibly do is modify the different components within this plug - perhaps to increase the temperature at which you could reactivate - and that might get over having hot baths. It's also possible that the way in which they formulated the plug means that, if you you shine a light onto the testes, it will specifically heat up the plug rather than the rest of the tissue.

Chris - Is it easy to get the plug in there in the first place. Would that be an injection into that duct into the vas deferens?

Bill - What they've done is they've introduced it into the duct of a rat. I think the human male duct will be larger and therefore the procedure will probably be even easier.

Chris - Is there any risk to the sperm from the chemicals involved in this. Could you damage sperm or introduce DNA changes into the sperm which might lead to birth defects, for example?

Bill - A bonus of this method is that one of the chemicals that are involved in dissolving the plug is also toxic to the sperm, and they make this point that you if there are any sperm that do manage to get through they are going to be incapacitated by this chemical. I don't think that it will introduce mutations, because the sperm has already fully formed and the the genetic material in the sperm is probably well protected. I think what it will do is it will render the sperm not functional, and you may want to wait after you've reversed the procedure before you try to conceive...


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