Disease breath tests, and Perseverance papers

Precision molecular scissors that can operate inside our cells to selectively target and dismantle the genetic material of the COVID-19 virus have been developed by researchers at the University of Cambridge. Dubbed XNAzymes, the scissors are themselves built from short pieces of an artificial genetic material called XNA. This folds itself into specific shapes that can recognise and target for cutting only the genetic sequences of  viruses, rather than any of the healthy genetic material that's meant to be in a cell. And by building sets of these molecular scissors that are effectively multi-bladed, they can be programmed to make cuts in the viral genetic material at several locations; so even if the virus adapts or mutates in one of the cut sites, it will still be disabled by cuts made elsewhere. Alex Taylor, from the Cambridge Institute of Therapeutic Immunology & Infectious Disease, CITIID, is here to explain how they've done this...

Alex - If you imagine the double helix like you sort of get with a short piece of DNA, sort of peeled apart into its two separate strands, one of those strands by itself can fold up into really a variety of different shapes. But in our case, the strings of nucleotides are made from these artificial building blocks. That's what makes them XNAzymes. They're strings of just sort of 35 or so of these. So that makes them about sort of 10 nanometers long. Just to sort of put that in context, it means you could sort of fit about five to ten thousand of these things across the width of a human hair. We know what the sequence of XNA that you need to sort of fold up into an active enzyme, but we actually don't know yet what the sort of catalytic core of these things looks like. But we know they have a sort of catalytic core with a kind of couple of binding arm sequences next to these that recognize the RNA. And in the study, as you say, we sort of took three of these XNAzymes, these molecular scissors and engineered them to sort of fold up into kind of pyramid like structures. So a bit more like a sort of three bladed blender.

James - How do you get them physically into the cells for them to then do their work?

Alex - Well, so for us it's very early days. We are just trying to understand whether and establish whether these things can actually have their kind of catalytic activity inside cells. So at the moment we've just been using this technique called electroporation. So this is where we give cells a little electric shock and that sort of opens up temporary sort of holes in the surface of the cell and allows the XNAzymes in. This isn't really a technique that we could use in a sort of realistic clinical setting. So in the future we want to explore sort of linking XNAzymes to things like the sort of fatty droplets as this is the kind of technology that was used for tthe Pfizer and Moderna RNA vaccines. But actually other researchers have shown that in the case of things like lung cells, it might be possible to sort of just inhale short oligos into the lungs in a fine mist and get them taken up into cells without having to rely on things like lipid nanoparticles.

James - And how effective have they proven to be in what you're trying to achieve with them?

Alex - So far we started off by sort of just in the test tube taking sort of short sections of the viral genome of SARS-2 and sort of linking these to kind of glowing dyes that allows us to kind of track the size of these RNA target molecules. And it was part of the exciting aspect of this technology is that we could rapidly generate a series of the XNAzymes really just within a couple of days of the genome coming out and sort of test whether they worked on these shorter fragments. And once we'd done that, we moved over to using the full RNA genome of the virus extracted from infected cells, tested them sort of with conditions that kind of mimic the inside of the cell. And again, once we saw that it was cutting, I was able to team up with a virology lab in my department who have a sort of safety level three lab and we challenge cells with a live virus. And we found that indeed once the cells have XNAzymes in them, they're able to inhibit the replication of the virus.

James - And just finally, Alex, could this technology be used for other diseases or recurrent infections?

Alex - Absolutely. So at the moment we're really only targeting RNA based viruses. But this includes some of the biggest kinds of emerging threats that we face over the last few decades. So things like Ebola, Zika, influenza, this kind of thing. So we certainly think that we should be able to know we're looking at sort of targeting some of these kinds of viruses. And really RNA viruses are really the big sort of scary group. About 40, 40 to 50% of emerging human infectious diseases are RNA based viruses. So, at the moment that's, that's where we're sort of putting our attention.

In the past, doctors used to prescribe a hot bath for some disorders, but now in some areas history is almost repeating itself with practitioners writing prescriptions for heating for patients with conditions that get worse in the cold. In an initial trial, the Warm Home Prescription pilot paid to heat the homes of 28 low-income patients to avoid the cost of hospital care if they became more ill. Those running the trial said it achieved such good results they plan to expand it to 1150 homes. So why is heating a wonder drug, and do the figures stack up? Cambridge University physiologist Christof Schweining knows all about how we keep warm and stay cool - he often puts his knowledge into practice as a highly successful marathon runner…

Christof - Well, I wondered exactly the same thing just before I came down to meet you. So I did a quick calculation on my trusty spreadsheet. So I looked up a patient in hospital for a single day, at least in A&E is about 400 pounds. And if you assume that you could target the people who want to have their homes heated appropriately, maybe you could stop 10% of the emissions. And then you imagine that perhaps if you were to get ill and be in an unheated house and get ill, that you would have a stay of perhaps two weeks or three weeks in hospital. Then it's worth, at least over the four months of winter, paying a hundred to maybe two hundred pounds a month off a fuel bill to do that. So I think it actually does make sense. I think it all depends on how well you can target this as a treatment.

Chris - What's the rationale though, for making people warmer in winter and that reducing their risk of disease? What's the link between being cold and getting health problems?

Christof - There are so many links going on here. One of the big links, which isn't talked about often enough, is the effect of, for instance, lying down in bed to stay warm over a prolonged period of time. That's an absolutely massive detraining stimulus. So imagine you've got somebody who is aging and relatively unfit. They've got some underlying disorder as well. If that person detrains as a result of lying down not being exposed to a gravitational field and also not performing exercise, just routine daily exercise, then they really do risk, at the end of a winter period or at least several weeks on into this bedrest, becoming so unfit that they struggle to deal with any kind of exacerbation of an underlying illness.

Chris - So this would be people retreating to bed early because it's warmer in bed than it is in the living room.

Christof - Oh, absolutely. I know I've just bought an electric blanket. Being in bed is a wonderful thing, but it's awfully a dangerous place to be really. Old people are particularly at risk here because the ability to sense your internal temperature reduces and your ability also to control the blood flow to your periphery, really to lock off the blood flow from the periphery to keep it centrally in the well insulated area that declines with age. So you've got old people and ill people who've got low maximal rates of aerobic work. They've got a compromised ability to sense their core temperature and also a compromised ability to restrict the blood flow to maintain the core body temperature. All of this adds together into a scenario where even if you don't have an acute serious illness at the point at which you take to bed, you may well end up at the end of a period in a position where you might need hospital care.

Chris - The rates of things like heart attacks and strokes also shoot up in winter. Can that be explained on the basis of what we know about how the body handles temperature?

Christof - Certainly. So there are some really simple acute effects that are well known. So when you get cold, you peripherally vasoconstrict, so you reduce the blood flow to the periphery. This pushes the blood centrally and as a result of that, you also get a rise in arterial blood pressure as well and somewhat of a thickening of the blood, so a haemo concentration. And all of that places a stress on the heart, which of course can exacerbate any kind of cardiovascular disorders. But there is some disagreement here as to exactly what the drivers are. So there are lots of things that go on when the weather gets cold and you take to bed, you become potentially a little bit depressed, a little bit less likely to exercise, maybe less likely to take care of yourself, to eat appropriately and indeed to drink as well. So all of these things add together to produce cardiovascular stress.

Chris - Do we see then the countries where it is warmer and warmer in winter, that they don't have this surge in winter mortality? Because that's the thing we see, isn't it? Every winter we see this so-called surge in excess mortality. Now some of that will be things like the flu, but many argue it is the cold that is killing people.

Christof - Ah, well this is interesting because you've caught me here on a set of data that I don't have. So I don't know whether the equatorial regions really suffer the same set of problems, but what's certainly true is if you look at different sets of societies, some are certainly much better adapted to cold weather. So if you look at the Scandinavian countries in particular, the infrastructure is such that the cold weather really doesn't present a problem. We are sort of stuck in the middle in that we have winters, which are sometimes quite cold, and so like the leaves on the line, we don't tend to take the necessary set of precautions.

Chris - You preempted where I was going with that, because I was going to say, well, there are many countries where it is much colder in winter than seven degrees today here in Britain, and we are not seeing the sort of surges in mortality that we see here. So it must be all relative then.

Christof - Oh, absolutely. I mean the bus stop is a really wonderful example. If you have a public transportation system aimed at a set of individuals who are more likely to be at risk from cold weather and then you don't have a regular bus service, you risk leaving them sat stationary in cold conditions for a prolonged period of time. And that really then presents a major acute risk. So something as simple as having a regular bus timetable that arrives on time, we just don't think about that. But things like that can be absolutely critical when looking at the risk of cold weather.