In Our Time - Free Radicals

Episode Date: November 1, 2018

Melvyn Bragg and guests discuss the properties of atoms or molecules with a single unpaired electron, which tend to be more reactive, keen to seize an electron to make it a pair. In the atmosphere, they are linked to reactions such as rusting. Free radicals came to prominence in the 1950s with the discovery that radiation poisoning operates through free radicals, as it splits water molecules and produces a very reactive hydroxyl radical which damages DNA and other molecules in the cell. There is also an argument that free radicals are a byproduct of normal respiration and over time they cause an accumulation of damage that is effectively the process of ageing. For all their negative associations, free radicals play an important role in signalling and are also linked with driving cell division, both cancer and normal cell division, even if they tend to become damaging when there are too many of them.With Nick Lane Professor of Evolutionary Biochemistry at University College LondonAnna Croft Associate Professor at the Department of Chemical and Environmental Engineering at the University of NottinghamAnd Mike Murphy Professor of Mitochondrial Redox Biology at Cambridge UniversityProducer: Simon Tillotson

BBC Sounds, music, radio, podcasts. Thanks for downloading this episode of In Our Time. There's a reading list to go with it on our website, and you can get news about our programs if you follow us on Twitter at BBC In Our Time. I hope you enjoy the programs. Hello, we'll be talking about free radicals. Free radicals are highly reactive atoms or molecules, and we can't live without them or sometimes live with them.

If all their electrons were paired up, they'd be stable. But some have one electron, which is unpaired, and are always looking to strip an electron from a nearby molecule to make up the pair. And that neighbour then takes one from another, and so it goes on and on. It's a chain reaction that's great for sending signals throughout our bodies or making long molecules such as for polythene, but it's also highly destructive if unchecked. And it's when the free radicals have free reign that they're linked to disease and cell damage.

Sometimes they've been blamed for the entire ageing process, so that's contested. With me to discuss free radicals on Nicolaine, Professor of Evolutionary Biochemistry at University College London Anna Croft, Associate Professor at the Department of Chemical and Environmental Engineering at the University of Nottingham and Mike Murphy, Professor of mitochondrial redox biology at Cambridge University. Nick Glenn, can you define what a free radical is?

Yes, it's really any atom or molecule that has a single unpaired electron. So usually electrons like to be in pairs. They're far more kind of comfortable as a pair. and if you have a single unpaired electron, it really wants to either find a partner and push itself onto another molecule or grab another electron from somewhere else.

And so it then forms a pair, but it leaves that other molecule with a single unpaired electron, which is why you have these chain reactions. Can you give us, listen to some idea of the number of transitions that might be going on this, in this industrial plant, which is inside our skin, and the size of the cells, the number and all that sort,

just give us a context there. Well, there are something in the order of 50 trillion cells in the human body. Inside those cells there are usually hundreds, if not thousands, of mitochondria. The mitochondria are the places where respiration is taking place, and respiration is where we're burning food in oxygen. And a lot of the free radicals that we produce are effectively reactive bits of oxygen. and we're producing a lot. We don't really know exactly how much,

but in the order of probably in a year, certainly grams, if not kilograms, worth of free radicals. What do we need to know about oxygen for this discussion? Well, oxygen itself, funnily enough, is a free radical in its stable state. And curiously, that's one of the reasons why it's not so reactive.

They don't always have to be reactive. I mean, it's easy to think of free radicals as being reactive. But oxygen is very reactive if you can feed it one electron at a time, and something like iron will do that, which is why things rust so easily. But mostly it's not reactive enough to yank electrons out from other places, and so we can have an atmosphere full of oxygen and coexist with it. And if you have them slightly more reactive forms of oxygen, you could never have an atmosphere that's composed of 21% of oxygen.

How much of this is going on? How much of this yanking, you use a word which is very helpful. How much of this yanking of electrons is going on as we're talking now? Well, it depends a lot on just how much oxygen there is. So in our cells, the level of oxygen is much, much lower than it is in the atmosphere. We're down around about 1 to 5% of the oxygen that's in the atmosphere is getting through to the mitochondria, possibly even less than that. And so the original experiments that were done to try and work out,

what's the quantity of free radicals that are produced? We're done usually in cell cultures sitting there under the atmosphere of oxygen. And the answer was lots and lots. You know, we would be producing if those calculations were correct in the order of hundreds of kilograms a year. But because the levels are so much lower inside our cells, we actually produce, you know, vanishingly small amounts probably. And that's why we now think in terms of signaling rather than just pathology.

Are we in an area where there's much more research to be done although a lot of exciting things are unknown? Yes. There's always a lot more to know, but I think in the case of free radicals, we're actually right at the beginning of our understanding of how they're acting in normal physiological circumstances. We've had 50 years of studying them as pathology,

as something going wrong, as something destructive, and they do do all of that, but we've had much less time, and it's much more difficult to study, to try to understand, well, how are they influencing the normal workings of the cell by signaling slight changes in the... I suppose the flux, the normal flux of how respiration is working,

how you're making new molecules, new building blocks, new DNA, new proteins and so on. All of this is controlled by a kind of steady state of production of free radicals. I hope we'll come back to signaling a bit later, but to cover a bit more basic ground. Anna Croft, how and when were they discovered these free radicals? So radicals were kind of known about or kind of hypothesized in probably the 1800s already.

And I think the breakthrough with respect to carbon-based radicals as opposed to the radicals of oxygen came in 1900 when a guy called Moses Gomberg created a molecule that seemed to be, incredibly reactive but yet still stable. And this was a trifenyl methyl radical. Lots of people had been trying to make derivatives. And he really hypothesized at that point that these were carbon-based species that would contain a radical and would be stable.

So Moses was quite an interesting person. He came from the Ukraine and moved across to America, to Michigan, in the late 1800s, and worked with some of the leaders in the field in Germany before going back and making this very stable molecule. He was originally trying to get a degree in physics,

and he turned up to try and get into the program at Michigan and was thrown out because he didn't know enough trigonometry, so he showed up three days later and was tested again and he'd learnt all that trigonometry so it was a really clever guy. When he discovered this pre-radical in the first place, was this thought to be in his area of science in that world? Was this thought to be a eureka moment? At last we've cracked something very important.

He's a new area of science. I think it was a new area of science and in fact on his paper where he put down, He actually, what was quite common at the time, put down something along the lines that says, I hereby claim this entire field for myself. Did you imagine a poet saying, I hear my claim all poetry of myself? Yes, something along those lines. Well, one-year-a-band, really?

Might have a good concept. Any minute, mine are right? But I don't think he actually realized how important this would all become. So it was fairly controversial early on, but then by, about the 1920s, people had managed to make methyl radical, which is one of the smallest carbon radicals that you can make. And building up on that work came radical polymerization, which then has obviously major industrial impacts.

So many of the polymers that we come across today, so PET, PVC, polystyrene, these are all products of radical chemistry. that was developed in the 1930s and just beyond. So the first application was in plastics? Yes. And was that taken up immediately? Did people say, whoopi, we've got a new material, we can change the world?

I think so plastics and polymerisation was developing, not just the radical form at the same time. And I think it was really during World War II in the post-World War II era that people really latched onto this was a new material or new way of. making materials that were very strong and robust because one of the very good things with the carbon-based radicals definitely you can make very strong bonds that meant that the material itself

was hard to break apart so very robust and useful materials thank you mike murphy it seems that radiation sickness promoted interest provoked interest in free radicals what was the connection there? The connection was very interesting. As Anna and Nick have explained, radicals are important because of their great reactivity and they're extremely reactive with all sorts of molecules. And this was used early on

from the work of Moses, Gomberg and other people like that, to develop this radical chemistry for polymerisation. But people didn't think it was going to be involved in biology. In parallel in the 1950s, people were very interested in the effects of radiation on the body. And it turns out...

Is it anything to do without a mumps? Exactly, because What was happening is there was a lot of funding available for people to try and counteract the effects of the atomic bomb and the hydrogen bomb and the effects of radiation on humans. So in the 1940s and 50s, people were exploring how does radiation damage the body. And one of the ways it does this is through radical reactions. What happens is this huge amount of energy coming from, say, a gamma ray, gets absorbed by the water in your body, and that makes free radicals out of the water,

because water is the dominant species in your body. and those radicals then go on to react with the protein, the DNA or the lipid. And those sort of reactions propagate through and cause damage. Now, that was obviously a pathology from an external source. But what one guy called Denham Harmon noticed, which was very interesting, was that the damage associated with radiation damage to tissue was quite similar to what he was seeing with aging and with some pathologies. So he suggested back in the 1950s that maybe some of the damage,

damage in the body, particularly that associated with aging, is due to a parallel process. At that stage, we didn't realize if free radicals were present in the body at all. But then this led on to other work where people in the 1960s found an enzyme called superoxide dysmitease that its only job is to stop radicals causing more damage in the body. So that suggests that they must be in the body. If he made the connection between free radicals and aging, yet you said they didn't realize. I said free radicals are all over the body. I don't quite get it.

Well, it was a leap of imagination on his part. So he was saying this damage is similar. Maybe there are free radicals being produced in the body, and maybe those free radicals are contributing to aging and pathology. At the time, there was no real evidence for free radicals being present, except in a few very specialized situations. Isn't extraordinary all this stuff going on, and then these free radicals pop up?

Who knows what's going to have next? No, my, let's go in with it. Mike, how do free radicals, Radicals damage cells. What happens is that, as Nick and Anna were saying, free radicals, their major property is extremely reactive. And that means that as soon as they're produced, they'll react with the fat or the DNA or the protein right beside them.

So they're not controlled or regulated. The other issue is that that just initiates a chain reaction because typically when a radical pairs up with another electron by stripping it off a protein or whatever, it makes another radical, which then can react with oxygen to form more radicals and so on. So you end up with this... When does that stop?

Well, what will happen is that that, in theory, could propagate right the way through indefinitely. What you have is antioxidants, which act to stop that. They quench the radicals by sacrificing themselves and reacting with the radical to form another radical that's stable and not reactive. Things like vitamin E and vitamin C,

the antioxidants we have in our bodies. they do that. And that way they stop this propagation of this damaging chain reaction. So it's always this kind of fight between the production of free radicals and these special protective mechanisms we have in our bodies to stop them causing more damage. So surely being oversimplistic, it's a fight, isn't it? They get going and the antioxidants come in and stop them. Absolutely. Without anybody tell them to do that.

Well, evolution selected the antioxidants. Yeah. Extraordinary. Nick, let's go back to, you want to say something. Well, one thing in relation to that. I wouldn't ask you about the theory of aging, so if you can wrap it up in a theory of aging, that would be great. Okay, well, one difference, I suppose, between radiation poisoning as it was seen in the 1950s and free radicals which are being produced in the mitochondria, which was first suggested in the 1950s, is the starting point.

So with radiation, you're starting with water and you split water and you get one of the most reactions. of all free radicals called the hydroxyl radical and that really will react with essentially anything immediately. It promiscuous radical. It really is promiscuous, yes. Now with breathing, you're starting at the other end. You're starting with oxygen and you're producing something which is much less reactive called the superoxide radical.

It sounds pretty destructive and in fact it's quite meek in comparison with the hydroxyl radical. And then there's another molecule in between called hydrogen peroxide which is not technically a radical but it's also quite reactive, moderately reactive. So you have these three intermediates between oxygen and water, and you can produce them from either end.

You can produce them from oxygen or from water. And if you've got radiation poisoning, you're producing them from water essentially anywhere. Whereas if you're producing them when you're breathing from oxygen, it's in a very specific location in the cell. Inside the mitochondria, they're far more mild in terms of their effects. So although there's this parallel between radiation, poisoning and breathing, I think the whole field had that in its frame for decades

that free radicals are just reactive. As Mike said, some of them are not. Vitamin C, vitamin E are radicals. Oxygen itself is a radical, but they're all pretty stable. So there's one thing that we've learned, I suppose, over the last couple of decades, is really big differences in reactivity. Anna, can I come to you about these antioxidants? How are they supposed to work?

Can you tell us more about those, please? So we've had already might describe, I guess, something like superoxide dismutase, which essentially kills off a radical process, I guess, more or less before it starts. And then I guess the more common antioxidants that people know about from, I guess, their diet and will be things like the vitamin E's and vitamin C. So vitamin E, for example, is a very fat, soluble vitamin that will capture radical. radicals within fat membranes, and so that way it will stop damage there. And it holds it in a very stable way for long enough for something like vitamin C, for example, to come and take it away. And vitamin C is very water soluble, so then can be moved along, as it were.

And again, holds the radical in a very stable way. And these stop this chain process by creating. this sort of more stable platform that can then be, I guess, more managed in terms of getting rid of it. And we've got lots of other sort of antioxidants that we may use either, for example, in food to make sure that food stays fresh for longer, yeah. And also, and things that we have, I guess, like in green tea, we've got sort of molecules. there which act as antioxidants. We have other sort of food products. Although it's unclear, I think, at this stage, whether all the antioxidants that people keep getting told they should

eat fruits and vegetables for are necessarily there in high enough quantities to make a huge impact. But what's very interesting is some of these antioxidant-like molecules do have different effects that we know contribute to stopping damage and aging anyway. So eat your vegetables, I think, is the moral of the story. Just in case from you. Well, no, I think they do have an effect, but whether it's purely an antioxidant effect is still up for debate. Mike, can we get back to this, can we get on to this theory of aging, which is very

prevalent, and brought up, Mike, and by herself, that it was said, this is similar to what was happening in vascular dementia and so on. And can we develop that and talk about it? Because it lingered on for a very long time. And it's still, it's contested, but it's still not entirely deleted. It's a very interesting theory because it's a very beautiful theory, very simple in its elegance. The original free radical theory of aging was that as you age,

your body is producing these damaging free radicals. And then what would happen is that free radicals would cause damage to your mitochondria in other parts of your cell. Then the damage parts of the cell would produce more free radicals. What did they think happen before they got on to free radicals? What was happening in the body before the year 2000? Well, this was actually a long time ago when people were thinking these.

There were many other theories for why aging occurred. Some of these were related to the number of breaths hypothesis that you could consume so many oxygen molecules or the rate of living hypothesis, which related to how fast you're metabolizing, the idea that we have that a mouse lives two or three years, whereas a human lives 80 or 90 years. So those were some of the ideas that rapid metabolism was associated with shorter lifespan than slow metabolism.

So can we get back to what you were saying before I rudely interrupted you? No, no problem. With that then, this idea that you would have this damage accumulation that then formed this kind of vicious spiral, that more damage produce more free radicals, it's more damage and so on. A beautiful theory, but the problem was that when you tested this in experimental animals, it doesn't seem to be borne out. and the original theory from Dunham Harmon was then extended in the 1970s saying it's the mitochondrial radical production. This was tested quite recently in various mouse models, and what they could do was that they could induce damage in the mitochondria and see what would happen.

And that remarkably produced very rapid aging. So people thought, oh, that's interesting. Maybe that damage means those mitochondria are producing more free radicals. But it turns out they're not producing any large amount of free radicals. So the issue with really understanding aging is to think about how you would know if something was causing aging. It's very easy to make something live a shorter period of time. All you do is if you want to damage something, you can hit it over the head. That's, we'll kill it off.

But the real test for hypothesis of something that causes aging is if you intervene in that and extend lifespan, we haven't really found any good ways directly related to free radicals and the simple idea of damage that extends lifespan. We've got many other ways that expend lifespan, and these tend to be by things like caloric restriction and nutrient sensing. And when we manipulate some of the genes involved in those processes, we can extend lifespan, and they don't seem to be related to through radical production.

Nick Lane, the idea of it being an explanation for aging held on for a long time is still not, it's contested but still not entirely eliminated, is it? Where is it at the moment? Well, it's in some kind of limbo. I would say. I think most people now would see free radicals as being a part of aging, but not the driving cause of it. And the simple reason for that is that you add antioxidants in the hope of interfering with the process. And they've never worked.

If anything, they tend to be slightly detrimental. And it's partly that the body response to them. No, you should definitely eat your vegetables. But you should probably not take large doses of vitamins. C or vitamin E or beta carotin or things like that. Because they can distort the balance, the body's natural balance, and you end up kind of suppressing the antioxidant enzymes, the proteins that detoxify these things.

You suppress them instead. So everything you do has a kind of a counter effect in terms of physiology, and that means it's very difficult to interfere in these processes. Now, does that mean that free radicals are not relevant to ageing or only just an effect of aging? I don't think, so I still think that there's some truth in the idea that free radicals are driving aging, but definitely interfering with antioxidants does not work. There's no question about that.

It's the signalling and it's the, I mentioned this word flux before, the rate of which we are. Let's do signal in signaling. And you're big on signaling, Nick, so let's go. Well, I think of it a little bit like a fire alarm, I suppose, or a smoke detector perhaps is a better analogy, that if you're over-producing free radicals, it's a little bit like producing a certain amount of smoke and you set off the fire alarm or the water sprinkler or whatever it might be.

And so that adjusts the system back to where it was. So without these signals, which is to say like the smoke, which might say you've been infected by a bacterium, you better respond now. Or you've had some stressful episode or something. you better respond now. These are the signals that say danger in effect. And if you cut them out,

then you don't respond properly to the danger and then you're more likely to be in trouble. And where does flux come in? Well, flux is, the way I think about it, I suppose, is we're breathing continuously. And as we're breathing, we are getting the energy to live, but we're also in the same process as making all the building blocks that we need

to replace the contents of cells or to make hormones or to everything that goes with living. And that's a continuous process over time. And all of this time, we're producing very small amounts of free radicals, almost undetectably low amounts of them. And they're giving a kind of a balance to how healthier cell is. It's on this kind of danger scale.

And gradually as life goes on, we get slightly further up the danger scale, be. It's not them by themselves. It's also everything else. How much energy do we have? How many of the building blocks themselves do we have? How healthier the mitochondria themselves? But I think the free radicals are part of that overall kind of health report for how a cell is doing. And if we try to fiddle with them, we tend to mess up that health report. Thank you. Thank you. Andercroft, another way free radicals use is in living things is with enzymes. Could you tell us about that? Yeah, so these are I guess not so free radicals. So there are loads and loads of enzymes.

Sorry? No, they're incarcerated more or less. So they, or in case within enzymes themselves, which use the power of the free radical then to do numbers of different types of reactions. and I guess we didn't quite realize how beneficial a lot of these processes were. It wouldn't have started until even, I guess, as late as the 1970s really. And there are processes such as with P450s which detoxify lots of material that if you've got toxins coming through, it will get rid of those from your liver by doing reactions there. We have things like cycloxygenases which make prostaglandins, which are very important in a lot of these signaling processes.

And then we have a huge range of other enzymes that, for example, are involved in antibiotic synthesis, involved, we think, in defense against viruses and in making a lot of the co-factors that we actually need for every day, life. And I think in terms of one of the most important examples of where radicals are absolutely essential in order to make the stuff of life is essentially we have this very specific enzyme called ribonuclid reductase, which in every walk of cellular life uses a radical. And that can be an oxygen-based radical as the others have described, or we have other types of radical that are generally mediated by metals in order to generate them.

And this enzyme itself takes precursors that are usually used for making RNA, which is a long polymer, which is used generally for making proteins, and it makes the precursors for DNA. And without these radical processes, we wouldn't have those building blocks for DNA. and we wouldn't have that sort of beautiful genetic storage that we have in all organisms that use DNA for that. Thank you very much. Mike Murphy, what's happening at the level of mitochondria?

Well, mitochondria particularly interesting, and it's an area that Nick has described elegantly already, that what we know about mitochondria is that they take the food that we eat and they strip electrons off that food and react it with the option that we breathe in. So about 95% of the oxygen that we breathe, then goes to mitochondria. And the reason that that's quite important in the terms of the radical production is that people always knew that mitochondria could produce radicals. The original idea

was that this was a damage process because it's a bit like a bit of copper wire with rubber insulation around it. You put an electron in on one end and it goes down the wire and the mitochondria are like that wire. And if you scratch the rubber, then some of these electrons might leak out, react with oxygen and become pre-radicals. But in some areas now, we can extend this a little, bit and show that it's not just random damage. It seems to be a controlled process. One of the areas that's very interesting at the moment is something called ischemia refusion injury. This occurs in heart attack or stroke. What happens is that when you block blood supply to the heart, electrons build up. And then when the oxygen comes flooding back in, say in the hospital where you

unblock an artery and blood comes back in to restore life to the damaged tissue, at those few minutes you get this burst of free radicals by mitochondria that caused the heart to be damaged. And we now understand a lot more of that process. So that in terms of the damage is the consequence of the cure? It's ironic, really, that a lot of the damage of the curse in a heart attack is that when you remove the blood clot

and the oxygenated blood comes back in, inevitably that causes a lot of damage. So that's caused that reperfusion injury where you re-perfuse the tissue is one of the most damaging aspects. We're really keen to try and understand that. But the assumption a few years ago was that that damage was random damage to the mitochondria. Now we think we understand

that that is actually a process that's normally used by mitochondria to produce few radicals, and it just gets abused during this extreme situation. And it turns out that process we think is involved in signaling, as Nick was saying before, but also as a way of sending on other pathways, such as in the inflammatory process, where the mitochondria are a key part of how the cell centers inflammation because that can send out signals saying that the cell has been infected or damaged, and that can switch on inflammatory processes. And coming back to the theory of aging, that may be one of the ways in which free radicals are affecting aging

through altering inflammation, which is probably a key player in aging. It's one of the sophisticated in there, isn't it? Nick, how are free radicals a component of breathing? Well, as Mike was saying, it's not so much the breathing so much as how we process oxygen inside the mitochondria. And as they pass down this wire, they can leak out. And we originally thought years ago with the original version of the free radical theory of aging that effectively a fixed proportion would escape that maybe 5% of the oxygen that we respire

would actually escape as free radicals and do this damage. And it's almost certainly a lot less than that, but it also varies. So, for example, if we're doing exercise, you're breathing maybe 10 times as much oxygen, and you would think then you'd have 10 times as many free radicals. But in fact, you don't have any more because the flow down, effectively the current down the wire in the mitochondria is just faster.

And so there isn't really a good correlation between the rate at which we're breathing and the rate of free radical production. And also it varies from tissue to tissue, and it varies from species to species. So birds and bats, for example, which live a surprisingly long time relative to their metabolic rate and their body size, tend to produce fewer free radicals

relative to equivalently sized mammals like a rat or something. So this is purely correlative, but we still have this feeling that there's something about the way in which we're processing oxen, over a lifetime, which is affecting the rate at which we age. And as Mike was saying, we've moved away from the idea of direct damage towards things like

inflammation, so indirect forms of damage. But there's still this rate factor. In other words, there's more research to be done. There's a lot more research to be done. Anna, how with enzymes do free radicals rid the body of toxins? Right. So in the sort of enzymes that I was talking about earlier, the cytocrine P450s.

These are really, really reactive. So much more, they are able to really pull off hydrogen from very unreactive molecules. And by doing this, they can incorporate oxygen and thereby make the molecule more soluble and thereby you can excrete that molecule from your body. So this is one of the ways where we can

remove toxic molecules from the body by doing this sort of oxidative process in order to get rid of them. Mike, how are free radicals used therapeutically? There are a couple of ways in which free radicals can be used therapeutically. One of the things about free radicals that we've mentioned is that they can actually cause damage to biological molecules.

So in some situations, our body's cells actually use free radicals to kill off bacteria. Sometimes of phagocel. are phagocytes that engulf bacteria. They actually produce some of these free radicals around the bacteria to try and kill off that bacteria. So that's one way in which our body naturally uses free radicals to cause damage. In addition, there are some drugs which we think could also be targeted to kill off particular

types of cells. Now, radiotherapy actually works because it produces free radicals that then if you can target the radiation to a particular area, the free radicals are produced there and kill off that cell locally and hopefully you're just killing off the cancer cell. We can extend that to cancer therapies in other ways. If you think about light often interacts with particular molecules and it will produce a sort of free radical form of oxygen called cinglet oxygen that's essentially a di-radical that's extremely reactive. And what you can do is you can target a drug to a tumor and then you can shine laser light at that drug and that will produce a burst of this thing called cingled oxygen

that then damages the cell. So you can have the drug in your body and and then you can localise it to the tumour just by having the laser. And the final version could be, in many tumours, the problem is that the core of the tumour has no blood supply. So inside that blood, inside the tumour, there's no oxygen. And that's still there and causing damage, but the traditional drugs which require oxygen to produce free radicals don't work. So there are some particular drugs that form other sorts of free radicals

that are only stabilised in the absence of oxygen, and there they're produced just in that anaerone. environment and the centre of a tumour, and there also wreak havoc and try and kill the tumour. So a number of different ways that we can use natural or artificial free radical production to enhance therapies. Well, this loops back to the original idea, one of the original ideas that it was to do with radiation. Of course, yes, it's all connected. Yeah.

Is there much more to be done in a therapeutic area? Do you think there would be much more ways discovered of using free radicals? I think there will be. Bearing a mind at the moment, our understanding of what goes on inside our bodies and inside cells is very crude. And the way we're using free radical... What's crude? It's crude. What's crude? What's going on? It's crude about what we know. And the way, the tools that we're using are relatively crude, because at the moment, our therapeutic interventions tend to be to kill off that cell.

So we select the cell and we try and kill off that cell. Really, if many of the important pathways in inflammation, for example, are involved in pathology and those involved mitochondrial or other types of free radicals, for those signaling pathways that Nick alluded to, we want to be able to directly intervene in those in more subtle ways, to say act as anti-inflammatories, for example. Those sorts of things were just scratching the surface about trying to develop new therapies.

So one aspect that I think could become very important is exactly how the mitochondria work between different individuals. So mitochondria have their own genes, and they're responsible for making part of the proteins, which are part of this wire for respiration, where we're passing electrons down the wire. But half of these proteins, more than half of these proteins, are encoded by genes in the nucleus.

And so they have to work properly together. Otherwise, the wire doesn't work properly. And there can be effectively slight differences in that wiring between different individuals. And that can affect the way the signaling systems work and the way that cells respond to it and the kind of stresses that they respond to or fail to respond to. it can differ between men and women,

it can differ between one tissue and another tissue, and it can differ depending on the diet. So lots of drugs will work very well for some people and be quite bad for other people, and those differences we've been thinking about in terms of genetic differences between individuals at the level of genes in the nucleus, where there's 20,000 of them.

But these interactions with the genes in the mitochondria, where there are only 13 protein-coding genes in the mitochondria, but they're so central to everything that the cell is doing, that very, very subtle kind of misinteractions there can affect the whole of the signaling and the whole way that cells work and then ultimately tissues work. And so that will be important, I think, in the future. Can I switch from the micro to the macro? How inseparable have free radicals being to evolution?

Well, they've been hugely important. To the origin of life, probably oxygen-free radicals probably not. particularly important to the origin of life. We turned about 2.3 million years ago for the origin of life. But oxygen appeared really in the atmosphere, or began to build up in the atmosphere from around about 2.2 billion years ago. And again, it's a long time ago. We don't really know exactly what happened. There were kind of calamitous stories of bacteria dying out as a result of being poisoned by oxygen.

There's some truth in that. They adapted to it. and we can see the way in which cells have adapted. We can see that in our own cells as well. That a lot of these systems that we can find in bacteria, Mike mentioned superoxide dismutase as an enzyme. It's all across the whole of life. Even things like body size,

there were periods where oxygen levels may have been higher, may have been as high as 30% in the Carboniferous period 300 million years ago. Again, we don't know for sure. But we see at that time giant dragonflies in the fossil record And there is some very nice work suggesting that one of the reasons they can get larger is that that effectively lowers the amount of oxygen in the in the tracheal tubes that are supplying oxygen to the tissues themselves to the flight muscles. Anna, your note, full of enthusiasm for the positive things that free radicals do

as if you want to shake off this thing that all they did was damage stuff. So can you tell us a bit more about that? So I guess one of the things, as I've briefly said about, the enzymes and some of these enzymes do predate the massive oxygen event that Nick was describing so we think that because they're based on iron and sulfur that they've sort of built up in these undersea vents where that was a very rich iron sulfur area and we see those traces in enzymes all the way through from I guess bacteria that are still hiding under there hiding from the oxygen um into humans themselves,

that actually the body has had to come up with very clever mechanisms for protecting these particular radical-generating species from oxygen. And this is part of the... Oxygen is the enemy, was it? In some cases, because oxygen will react with any free radical. And if you have a beneficial free radical that is helping you maybe to break down metabolic products

or generate a new type of compound that you want as part of metabolism, then you need to stop oxygen from destroying it. And certainly some of the enzymes they even harbour a free radical on the protein itself. And this needs protection from oxygen because otherwise the protein itself degrades. Are there any particular area? is that free radicals, in which free radicals are having a positive role, areas that people listening would know about commonplace stuff.

I think the... I mean, I'm looking for commonplace stuff, Mike. Okay. I think the idea that how new types of drugs will intervene in this, so many areas of new drug development are based on trying to understand these processes and intervene in subtle ways. We mentioned heart attack and stroke. Many of the new types of drugs that have been developed

are trying to understand those processes. and come in with new interventions that will block some of the damage caused by free radicals. And related to that, I think new drugs based on inflammation will also be involved in trying to understand those signalling processes caused by free radicals. So those are the areas that I think will be hopefully commonplace in years to come, but they're just emerging over the last few years. So what we're talking about, do you want to say something? Oh, well, I guess one of the things is with these radicals actually damaging bacteria as part of infection.

So this is, I guess, a very tangible, positive where you have the radicals coming in and they're actually doing something for the body. And analogous to plastics we were talking about earlier on. Oxygen radicals are used to make the long-chain polymers that give lignin its strength in the bark of plants, for example, or the connective tissues of plants. And collagen, which is really being called the tape and glue of the animal world, but it basically holds all animals together.

it's a free radical process that's building these strong cross-links between them. So they've been used in an extremely positive way. And for the most part, they don't cause any serious damage. It's only when there's conditions like a heart attack or something where it's out of control. Or the very gentle process of ageing, which is kind of uncovered by the unusually long human lifespan. Finally, Mike Murphy, I wait the beginning of the understanding the place and worth of free radicals.

Is there a lot more to find out? I think we're just starting because it's a huge leap to go from the chemistry in a test tube and the experiments we've done up to now with, say, isolated enzymes and isolated mitochondria. To really understand how that works inside a body, inside a patient, that's a real challenge, and we're only just beginning to understand those processes now. And from the body and the patient of society? Exactly, yes. Well, thank you very much.

Mike Murphy, Nick Lane, Anna Croft. Next week, Mariantoinette, sent to the guillotine in 70 and 19. French Revolution. Thank you very much for listening. And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Melvin and his guests. Well, thank you. I mean, I understood that. Amazing. What an education I got. I just have to remember it.

That's the second bit. Now, what do you think? Did we miss out? Did you miss out? Did we miss out? Anything essential? I guess the pre-radical chemistry, one thing that people outside might be interested in is that it's actually a key part of, say, how the ozone layer works, how smog is produced. So a lot of this other aspects of radical chemistry occur in the atmosphere that we've completely bypassed. I don't know whether Anna being a real chemist would know more about these things. Yeah, I'm not an atmospheric chemist, but I mean these are extremely important processes.

And we see sort of, as you mentioned, the ozone layer, which I think is one of the big ones where that's come into play. but also I guess as part of air pollution, so radical formation there and the worries behind what that might be doing to both people, I guess, and other molecules, generating all sorts of other things. I think it was the chloroflora-carbons and their disruption of the ozone layer. That was because of radical chemistry going up high in the atmosphere that was disrupted by these molecules.

So this takes us back to the radiation, because obviously you've got much more radiation up in the atmosphere that allows those processes to happen and allows that energy to break the molecules apart in order to generate the radicals. One thing you touched on as well, in hydrothermal vents, these iron and sulphur conditions, they produce radicals as well,

and in the absence of oxygen, they're extremely important in organic chemistry in making, crafting new molecules and so on. So it's only when you have oxygen there that it becomes really dangerous. And most hesitate to say primitive cells, but very early bacteria are absolutely stuffed full with these iron sulfur complexes. They're like little minerals almost.

And they work brilliantly if you're in a stagnant conditions where there's no oxygen. And it's really, we still use them. I mean, it's extraordinary that we still have in our mitochondria, all these little iron sulfur clusters. You know, there's tens of thousands of them in every single mitochondria. And they're dangerous as hell when you've got oxygen around. but we need them because you've got to feed oxygen electrons one at a time and iron is really good at doing that.

And so they've stayed there for that reason. But you have this tension between carbon, which wants to have two electrons at a time always, an oxygen which can only take one electron at a time. And effectively life can only work if you're going between this one and two electron chemistry. And so it's there. It's a really difficult tension right at the heart of everything. One interesting point moving on a slightly different topic

is the free radical theory of aging. It's been a fascinating theory. And often you can think of theories as not just being right or wrong, but being rich and productive. And the free radical theory of aging has been very productive because it's forced us to do very interesting experiments.

And as we refine our understanding, it's helped us do that a lot. Even though the classical original view is almost certainly wrong, it's actually inspired very many new interventions that we're trying to understand. And that's been a really,

interesting insight from Denham Harmon all those years ago. Another aspect to that in terms of the free radical theory of aging is a lot of the measurements were done at Normoxia, which is to say under the atmosphere of 21% of oxygen. And you can measure, on a bench, and you can measure free radicals under those conditions. But for decades, if you put those same cells at one or two, three, four percent oxygen, you know, you can't measure any free radicals. We can now because we have more sensitive technology. We really have no idea do you need grams of these things or milligrams or micrograms.

But a theory has been built on evidence which was the best that we could do and is good, but it doesn't really tell us, you know, we don't actually know if there's a correlation between these grammar quantities of free radicals or microgram quantities of free radicals. Does it matter that it's thousands of times less in terms of the total rate of formation of these things? We don't really know that kind of question. So I won't say it's misleading, but a whole field of medicine can be kind of questionable

because of the conditions under which it was done, and those conditions are effectively the only practical conditions under which you can do it. Yeah, so we also, I guess, one of the other things is this complex interplay of different molecules as well. So interestingly, vitamin E, which we talked about earlier as an antioxidant, under certain conditions, if you haven't got the right molecules in place, can also be a pro-oxidant.

That means it will help to oxidize and damage things. So, again, the conditions under which you measure things, the complexity of the system really matters in being able to understand the exact processes that we see happening. What I liked about, and I didn't like, and I, because you were so interesting, and we're talking about it, was how do you do this? How do you measure this? and these are so tiny,

and these trillions are rather daunting at the start. Quite exciting, but quite daunting. How do you measure it? What are you doing? Well, it's very difficult. But what you can do is you can set up situations in isolated systems where you have very sensitive detection molecules, maybe a fluorescent molecule.

Extending that in vivo is quite difficult because a fluorescent molecule means you can shine light on it, emits light at a different wavelength that you can detect. That's how we would do it in cells or in isolated bits. of cells. In vivo, light can't get into our body so easily. So there are a few other methods that we can use. These tend to be indirect because the free radicals by their nature are very short-lived. So what you tend to do... What short-lived? It could be milliseconds or microseconds. Oh, that's short-lived. So that's quite short-lived. So if they're generated inside one part

of a cell, they would usually be disappeared before they've diffused more than a few hundred nanometers or depending on the lifetime. So what you often try and do is you detect them indirectly by a footprint that they would leave behind, either damage or a change in a local reaction. And from that infer what was going on in vivo, in the patient or the experimental animal. And this is one of, I guess, the difficult things is that you see a lot of the free radical damage

under certain disease conditions. And as we said, so even in things like diabetes, you can see that footprint, but it doesn't necessarily mean that the radicals caused the disease, it's just there is, there are other processes working alongside, but we can still measure the footprint and this is why people think that, or can come up with theories that say, okay, radicals are involved in this, that or the other, but it's all correlation, not causation. And you try and interfere in the process by throwing in antioxidants and they don't work. They don't work as you expected them to work. And the reasons for that are really very subtle.

It boils back down to all of this signaling and the responses, and they throw a signal of danger in the cell responds to quash that danger. So, you know, throwing an antioxidant can be the worst thing to do sometimes. Are you thinking of an improvement in technology, which will improve technological improvement you're looking for? We are, in our lab, for example, we spent a lot of our time trying to develop better techniques to measure these things in, for example,

some of the work on the heart attack. That would relied on mass spectrometric techniques that we were able to develop to be able to see what was happening inside the heart during a heart attack. So those sort of things and always new techniques and new approaches give us new insights and allow us to fine-tune our ideas a little bit better. But always better techniques and better measurements are a huge benefit in all areas of science, especially in these areas. And always the cross-comparison between, I guess, whole systems as you're working on

and the model systems in order to build up at least the tiny picture to work out what's happening as well. Well, the producers, gnawing at the bit, at the door, knowing the door. I need to offer you tea or coffee. Would you like to your coffee? Oh, a cup of tea. Good, thank you.

These biscuits are fantastic. Oh, excellent. I love. I think I love. In our time with Melvin Bragg is produced by Simon Tillotson. Hello, it's me, Mae Martin. I hope you enjoyed the podcast you just listened to. Can I recommend another podcast that you might enjoy?

It's called Grown Up Land. And it's a podcast for people who find the adult world. A bit much. Every week, me, Bisha K. Ali and Ned Sedgwick and tons of other guests, try to get our heads around stuff that confuses us like sex, very confused by sex, fear, food, and friendship. I'm running out of time for this ad. Ned, how would you sum up the podcast? I'd say it's like a guidebook for people who don't really know where they're going or where they've been. Great. Thanks, Ned. That's grown-up land and you can find it on BBC Sounds.