New Alzheimer's treatment, and mussel memory

A new contraceptive inspired by Roman history and shellfish is being investigated by scientists in Sweden. Many women currently use the birth control pill, but some would prefer to prevent pregnancy without altering their hormones. Ulrike Schimpf has been developing a way to use the substance chitosan - a sugar-based molecule that comes from the outer skeletons of animals like shellfish - to reinforce the natural mucus barrier which forms in a woman’s cervix and can temporarily block the passage of sperm. Professor of Reproductive Physiology at the University of Cambridge, Bill Colledge, has been looking at the study results for us…

Bill - They have effectively developed a barrier method to prevent the sperm from reaching the egg and causing fertilisation. And they've used a substance called chitosan, which is a very long sugar molecule. And it's actually derived from chitin, which is present in the exoskeleton of insects and crusta. And what the substance does is it binds to mucus within the female reproductive tract and it effectively plugs the entry of the cervix. But interestingly, it's been known for a long time, the Romans used to use half a lemon placed up against the cervix as a type of diaphragm to block the penetration of sperm. And they use this as a contraceptive.

James - What is it about the chitosans that make them so fit for this purpose?

Bill - They're natural substances and they've been used in a variety of different applications, including clinically. So there's a lot known about their safety and efficacy. The mucus within the vagina does change throughout the menstrual cycle, and some people use this as a normal form of contraception. They monitor the mucus, it's called the billings method. And what women can do is they can monitor the viscosity of the mucus throughout the cycle. And at the time when they're ovulating, the viscosity changes and it becomes more sort of like it's described as egg white. And at this time the sperm can actually penetrate through the mucus and can get through the cervix and can reach the egg. So effectively what this study is doing is adding something into the vagina that will bind to the mucus, change its thickness, and therefore stop the sperm from penetrating.

James - You mentioned that this is a barrier method of contraception. I wonder if I could ask you the benefits of barrier methods over different methods of contraception, more hormonal based ones?

Bill - It's going to have less side effects. So women take the contraceptive pill, which is either progesterone or progesterone, a little bit of estrogen, mood changes and things like this. Whereas this is not going to cause that there's no hormones involved.

James - I mean, it's all sounding very promising. Is there anything that you notice that might halt our enthusiasm?

Bill - Well, the authors discuss the various caveats and the limitations of the study. Obviously it's very early stages. One of the main caveats is that the work that they did was done using a female sheep as a model, and the vagina and the cervix of the sheep are slightly different from the humans. So there may be some differences when they tried to translate it into doing it in women. They also point out that they haven't taken into account the effects of sexual intercourse, which is a very physical thing, so that might limit its efficacy. The other thing that they don't look at is how long it lasts. So they administer it and one hour later they show the effects. And I think the effects certainly last four hours, which is the limit of the study, but they don't know how long it'll last thereafter. So I think they're probably going to, if you use this, you may have to use it prior to any sexual intercourse, every time.

James - And a 98% efficacy rate. Could you contextualize that against other contraceptive methods?

Bill - The hormonal contraceptive methods are very effective. They're up in the 90% if used correctly, so it's as effective. Of course, they've only shown that it blocks sperm. They haven't looked to see whether it affects the ability to get pregnant. So although 98% sounds very, very effective, you're still gonna get 2% of the sperm penetrating. And of course, you only need one sperm and one egg to result in fertility. So until they actually check what effect it has on fertility and live births, we don't know whether that'll be sufficient. But by analogy to the hormonal contraceptives, which are of a similar sort of efficacy, you would think it would be as effective.

To the aquatic realm now, and mussel numbers are a good indicator of the health of a river. And Cambridge University zoologist Isobel Ollard set out to replicate a study from over half a century ago on a stretch of the River Thames near Reading to see what had changed. Alarmingly, mussel numbers were down 95%, with some species disappearing completely…

Isobel - Muscles are one of the most threatened animal groups globally. But in the UK we really have very little information about how they're doing. And this study, which we replicated, was carried out in 1964 and it was one of the first properly quantitative surveys of muscle populations anywhere in the world. And it found, for example, that freshwater muscles contribute over 90% of the biomass in the river Thames, in the riverbed. So we wanted to return to that site and use the same survey methods, find out what's changed in the intervening period.

James - And other than that headline stat of 95% population decrease, what were the other key findings of your study in comparison to that one 50 years ago?

Isobel - So we found that one species, the depressed river mussel, has disappeared completely from the site. So although we found a few shells, we didn't find any live muscles of that species. And two other species have declined really sharply. So the duck mussel is down 99% and the Painter's mussel is down 97%. And those are both species, which are typically seen as common. We also found that individual sizes in the muscles have changed. So they're growing more slowly now than they were in 1964 and they're reaching sizes which are about 10 to 35% smaller than they were nearly 60 years ago.

James - All sounds quite worrying.

Isobel - Absolutely, yeah. And really for two reasons. So the first being that mussels are often viewed as indicator species about the health of an ecosystem. So if mussels are declining, that's kind of bad news, which suggests that the habitat quality more generally is probably deteriorating. And the second reason is that mussels are really important in the ecosystem. So they're described as ecosystem engineers because of the roles that they play in underpinning the ecosystem more widely. So they're filter feeders. They take in algae and other organic particles from the water column and help to keep the water clear and a single muscle can filter up to 40 liters of water in a day. So you can imagine the amount of water filtration that's going on across the river and we know that having a high density of muscles is associated with high riverbed biodiversity.

James - So what's the cause? What's behind this dramatic decline?

Isobel - One clear reason that we found is the fact that this site's been invaded by zebra mussels, which are a non-native species to the UK, which are now found in fairly high densities in the river Thames. And they weren't present at that site in 1964. And they're a really problematic invasive species so they can settle on hard surfaces, including on the shells of native muscles. And that means not only do they compete for food with those muscles, but they can also smother them and ultimately stop them from opening their shells at all. There's probably also been wider ecosystem degradation, so things like pollution. We also looked at the level of nutrients in the river and we found that the level of particularly phosphate has declined a lot in the intervening period and that's probably due to tighter controls around sewage releases. And while that's good for the ecosystem generally because less nutrients means less chance of developing harmful algal blooms, that could be potentially bad news for the muscles in that it means less food availability for the mussels and we think that might be contributing to their slower growth rates.

James - So what do you propose we do about this? Is there anything we can do about this?

Isobel - So I think one of the really key things that comes out of this is that we need more monitoring, especially for species which we think are common. We really have no idea how widespread this picture might be across the UK. In order to kind of pin down the causes and design better interventions and to conserve these species, we need to do more monitoring more widely and across more species.