Full episode transcript below. Beware of typos!
Nick Jikomes
Dr. Maayan Levy. Thank you for joining me. Thank you for having me. Can you start off by just telling everyone who you are and what your lab works on? What kind of what kind of science that you do, sir, so I am an Israeli scientist. I was born in Israel and I was trained in Israel. I did my masters and my PhD at the Weizmann Institute of Science in the level of Llanelli now,
Maayan Levy 4:29
studying the microbiome, I came to the University of Pennsylvania in 2018. And I've opened my lab in the microbiology department and generally my lab is interested in studying questions that are related to the microbiome intestinal immunity, how the communication between the gut and the bacteria is happening.
So we are we're mainly focused in the gut and how this kind of interaction is influencing different human diseases.
Nick Jikomes 5:00
And how did you get interested in that general subject? Were you? Were you always studying this? Or were you studying something else and then kind of got into this?
Maayan Levy 5:11
So I think that's, you know, we, about like 10 years ago, there was a major focus and shift into the microbiome. And I think this mainly happened because, you know, we understood that our genomes cannot explain everything, there are diseases, and they cannot be explained by alteration
Unknown Speaker 5:35
or natural combat or genome specializing there must be something else will be something else is our microbiome, and products
Maayan Levy 5:47
are much larger than the amount of genes that are contributed by by us by the host. So the the microbiome is has been over these past years shown to be relevant in basically any aspects of human physiology and human disease. So now you can connect the microbiome to almost any disease from neurological diseases, cancer, aging, different metabolic diseases, lung diseases, and basically everything. So we know that the microbiome is super important for many, many aspects of our lives.
Nick Jikomes 6:23
Yeah, I mean, that makes a lot of sense. Just, you know, when you think about how, how numerous, these microbes are, in terms of the number of cells and the number of genes, yeah, it really does make a lot of sense.
Maayan Levy 6:35
And it's not just a number, it's also how close they are. So if you're thinking about the gut, the the amount, that this huge amount of bacteria that we all have inside of us is like is located so close to what we know and need to maintain a sterile tissue. So they, they're, they're so close, or they're, you know, they we are sensing them constantly, we have to constantly react and respond to their presence. But on the other hand, we need to make sure that we don't constantly have an inflammatory condition and a constant response towards the bacteria.
Nick Jikomes 7:10
Yeah, so that means, you know, it's very interesting. On the one hand, you have to have this sort of exquisite sensory system to constantly detect and identify these microbes. And yet, it somehow has to discern that they are not bad or not always bad, so that we don't have this constant sort of immune reaction.
Maayan Levy 7:28
Exactly. And so with this, I think that the way I say the major cell cell type that is mediating this protection, or sensing is the intestinal epithelial cells. If we're focused on the gut, obviously, there are microbes outside of the gut, basically, everywhere that our body is exposed to the environment, the skin, the lung, the reproductive tract, but my focus is in the gut. So I can I can say that the cell type that I think mediated interaction is intestinal epithelial cells, these are the cells that line the the gut, so that they are the cells that see the microbes and what they produce first. And if you're thinking about sensing mechanisms, by now, we know that there are several types and several families of receptors that can sense the presence of bacteria. And during my PhD, I actually worked on one of these sensing platforms that is called the inflammasome. And I worked specifically on an inflammasome that is called NL RP six, it is called an RP six, because the sensing component to it is an NLR portents, this called NLRB six, we call it the NLRB six inflammasome. And this was discovered back in 2012, by my PhD mentor, Dr. Ron Allen oven, what he found is that this specific inflammasome is expressed in epithelial cells in the gut, and that in the absence of this sensing platform, the mice develop an abnormal microbiome composition or a dysbiotic microbiota composition. And more interestingly, what he found is that this microbiome made the mice more susceptible to different inflammatory diseases IBD, but also diabetes, and even colorectal cancer. So if you if you do not get out, if there is no sensing, the microbiome becomes abnormal, the composition is not what it used to be. It's not it doesn't look like a healthy composition. And the function of bacteria, more importantly, is altered this one.
Nick Jikomes 9:32
I see. So if you if you disrupt the ability of the cells lining the gut to actually sense the bacteria that are present, they presumably can't figure out which bacteria are which. And the general consequence of doing that if you completely disrupted as the microbiome composition is different, and you're more susceptible, at least rodents are more susceptible to all kinds of different diseases. Sure.
Maayan Levy 9:56
Yeah. That's exactly this. And so this was the A battery the initial observation, what we then did in subsequent studies to show exactly how it happens, we found that the microbes can influence the activity state of this sensing platform. And downstream to the sensing platform, there is secretion of inflammatory cytokines, il one beta and il 18. And we found that downstream to these cytokines, there is a transcriptional program inside intestinal epithelial cells that leads to a secretion of antimicrobial peptides. And when you disrupt this, you disrupt the, the secretion of these small peptides that are anti microbials. And if you don't have these anti microbials, then the community of bacteria goes wild.
Nick Jikomes 10:45
I see. So, so there are systems that these cells are connected to, which probably regulates the type of anti like natural antibiotics, basically, their bodies, and how much we're making. And if you disrupt that you make too much or too little or the wrong ones, it just screws up what kind of bacteria are actually,
Maayan Levy 11:04
exactly. So you're you shift the balance somehow when it becomes abnormal, and more likely to develop different intestinal diseases.
Nick Jikomes 11:13
And to what extent so when we think about the body's internal ability to sense and identify bacteria, how much of this are we born with, like how much of the knowledge is innate and how much of it has to be learned as development is happening.
Maayan Levy 11:31
So we are mainly focused on the innate immune system that we are born with, I don't think it needs to be trained. But if you're thinking about the, you know, the coevolution of bacteria, and the human holes or mice, then we're born sterile and then we acquire the bacteria. So, I as far as I know, there is no activation of this sensing system. In You know, before we are born when we are sterile, and then after we are born, and we acquire the first bugs, then we start sending and reacting and maybe learning what we need to respond to and what is a friend.
Nick Jikomes 12:11
I see. And so there's this distinction between the innate and the adaptive immune system that gets made in immunology. Can you just sort of explain what that is for people at a very basic level?
Maayan Levy 12:22
Yeah, so the, the immune system is divided into two main arms, the the adaptive immune system and the innate immune system. When we're talking about the innate immune system, we talk about receptors that can detect different molecules. And they, they these receptors, they we all have the same ones, they don't undergo any recombination, in contrast to receptors of adaptive immune cells, mainly B and T cells. So what we are born with is what we have we there is no. Okay, generally, it thought that the innate immune system doesn't have any memory capacity, in contrast to an adaptive immune system or an adaptive response. In if you challenge with a pathogen that is, then the adaptive immune system will respond. And then in a secondary challenge, the response will be even larger or more robust. This is something that doesn't happen when, when something is sensed by the innate arm. So it's a it's a more basic, maybe or more streaming, stereotype. Yeah, maybe more primitive response?
Nick Jikomes 13:47
I see. So in general, I mean, there's probably a lot of complexity and caveats there. But in general, right, so we're sort of born with this innate immune system, it's the part that like, is basically encoded in the genome, it's sort of ready, ready to roll.
Maayan Levy 13:59
It's hardwired.
Nick Jikomes 14:01
And then, so that, that that is part of the sensing mechanism for how these gut epithelial cells and the linings of the gut are sensing the identity of the bacteria. And so what about the bacteria? Do we sense like, how does the body tell a bacteria from a human cell?
Maayan Levy 14:18
I think that's the question is even more interesting than the question that you're asking. Now, how can the system distinguish between good bacteria and bad bacteria? Yeah, interesting. It because if you're thinking about these, so these sensing receptors, they can be either on the membrane of the cells, and since they're basically the gut lumen, or they can be in the cytoplasm of the cells, and then they will send something that will enter and can be recognized inside the cells. If you're thinking about recognition of bacteria by these kinds of receptors, then there are I think we need to make a distinction between commensal bacteria and pathogenic bacteria. So if we're thinking about the gods, then we have the The line of epithelial cells and they are inside the lumen inside our tube, there is feces and bacteria inside it. But in between epithelial cells and the fecal matter, there is a layer of mucus. And generally this mucus layer is preventing bacteria from getting really close to our PCR cells. So commensal bacteria, they usually cannot penetrate and get physically very close to epithelial cells, we have this this border fossa genic bacteria, on the other hand, they have mechanism mechanisms through which they can penetrate this, this mucous layer and get physically connected and physically really close to epithelial cells so they can be sent to a physical interactions. I think that when we're thinking about commensal, bacteria, the the gut bacteria that we all have in our gut and are not necessarily considered pathogenic, then we're talking about these, these boxes cannot get really close. So we need to be able to sense something that is more likely being secreted by these bacteria. So it can, it can be secreted from bacteria and get closer and even enter intestinal epithelial cells. So when we're thinking about this, we can we mainly call these small molecules metabolites. So these metabolites, microbial metabolites can be sensed as well,
Nick Jikomes 16:23
I see so so I'm imagining, imagining a system here in ecology where, so you said, you've got the lining of the gut, and then you've got bacteria, but they're not touching generally, there's this protective mucous layer literally physically, you know, protecting and creating a barrier between those two populations ourselves in the bacteria cells. And if I'm hearing you correctly, the difference between a pathogen something that's bad for us and commensal bacteria, which is not, isn't necessarily like an intrinsic difference between them, it's simply whether or not they get too close. So, so could good bacteria even be bad if they if somehow if that mucous layer breaks down or something like that.
Maayan Levy 17:05
Yeah, exactly. So there are cases where commensal bacteria of the bacteria that we consider good, they can become more pathogenic. And other other conditions where it's, it's many conditions that our immune system cannot recognize them, and not cannot maintain this balance with the antimicrobial peptide and the cytokines that are being secreted and antibodies that are being secreted into the rumen. And under these conditions, where the immune system is breached, then we can these commensals can become pathogenic. The difference between commensals and pathogens is one of them is the location in, you know, in relation to epithelial cells, but it's not the only difference was the genic. Bacteria have all kinds of toxins and different factors that they can secrete into the cell, they have different machineries to that allow them to become pathogenic and cause the disease commensals usually do not have these, these programs.
Nick Jikomes 18:04
So So you've got this mucus layer, sort of protecting the body, not letting not letting any of these bacteria get too close. And there are different things, different molecules that these bacteria secrete some of those are sensed by the cells of the gut. Is there any are there any general patterns as to what kinds of molecules are being sent to like, what are these things? What what kinds of things are they?
Maayan Levy 18:28
So I think it's the million dollar question. We know that in the gut, there is a huge, huge amount of these small molecules are metabolites. And the function and the identity of the majority of them is completely unknown. We don't know what exactly they are, we don't know exactly how they're being sensed, we don't know what happens downstream or after these molecules are being sensed. But over the last few years, we we and others have studied studied few of these examples, few of these metabolites in great detail that now we understand that some of these microbial metabolites can be sensed by different parts of the innate immune system or different immune cells, and downstream to them, many things can happen. So if short chain fatty acids that are the from fermentation products or fibers that are fermented by bacteria, we cannot metabolize these kinds of molecules. Then, they can downstream lead to secretion of different immune different cytokines. The function of many of these metabolites, again, is completely unknown. We found specifically during my PhD, a few of these metabolites that can activate an immune response and other metabolites that can suppress the immune response to the the inflammasome complex that I've mentioned before. So some of these metabolites can can activate or support an immune response and some will dump and, and an immune response. But again, the majority of the metabolites is completely unknown.
Nick Jikomes 20:12
I see so so things are mostly unknown here. But there's at least two very broad classes of molecules that seemed to be at work here. One are molecules that we sense in order to regulate the immune response, either turn it up or turn it down. And then presumably, a lot of these things are actually directly ingested as nutrients as well. Is that Is that true?
Maayan Levy 20:32
Yeah, that's exactly true. So the, the, in addition to the, you know, the regular function, or the function that we would first think of when we think about bacteria, which is processing, and they just general food, and different different molecules that can be produced as a result. We were concerned. So maybe, let's phrase it differently, we can sense breakdown products of food that we eat, these products are either being digested by us by ourselves or by bacteria. And we can also send these small molecules that are indicators of some microbial activity in there from microbial origin. So if we think about different components of bacterial cell wall or different metabolic products of bacteria, that tells us, hey, now there is a very active microbial community, you need to do something about it, maybe you need to secrete many of these antimicrobials to to reduce their numbers. Maybe they're getting too close to us to the cells, maybe we should, you know, produce more mucus to push them a little further away.
Nick Jikomes 21:51
Yeah, I did want to ask you more about that mucus layer? It's, it seems very important. Obviously, I imagine that there are people and animals that can be put into situations where they're making too much or too little. What, are there any, are there any disease states that maybe people will be familiar with that involve problems with that mucus layer?
Maayan Levy 22:14
Yeah, so So one, one example is, is inflammatory bowel disease. You can, you can have, we do reduce production of mucus, this enhances the inflammatory state in the gut, if there is less mucus, then bacteria can get closer. And it enhances the immune response. So any, almost any inflammatory condition in the gut can have some kind of alteration in your co secretion. Some bacteria can degrade mucus, which makes the situation a bit more complex.
Nick Jikomes 22:53
And, you know, one of the things that's interesting here, so So there's two things I want to discuss in terms of things that we put in our bodies that are probably changing the microbiome composition. One is diet, and the other is antibiotics. So let's just take those one at a time. And consider Can you just talk a little bit broadly speaking about how how sensitive the microbiome and its composition is, to what we eat? If you shift your diet in any significant way? How, how sensitive is that microbiome going to be to that?
Maayan Levy 23:29
Very sensitive, so the microbiome receives many environmental signals, one of these environmental signals or lifestyle, lifestyle signals is diet. So when we shift our diet to a different diet, that microbes will change, they, you know, the microbes, see what we eat, they metabolize it, they, they, they grow, or they die in response to it so that the Composition Composition definitely changes. You know, there are many cases in which people you know, they travel to different countries, their microbiome shifts, but then when they will return return to their country of origin, then they will go back to their lifestyle, and the microbiome will gradually shift back. So it's, it's, we can say that genetics influences the microbiome and the composition, but it's also diet and lifestyle in this factor, in contrast to genetics is something that we can we can influence. Antibiotics, deplete the microbiome. There has been a study from the inov lab from a couple of years ago that shows that following antibiotics treatments, if you give probiotics it takes even longer for the original composition of the microbiome to return and to recolonize.
Nick Jikomes 24:58
So yes, it say more about that. So you're saying using antibiotics, you sort of wipe out or deplete significantly the microbiome. And then people these days are often now using probiotics to replenish it. But you just said it takes even longer when you use probiotics in these cases to replenish the old.
Maayan Levy 25:15
Yeah, there are some cases where they've shown this to people that the took probiotics, it took them even longer to to get back to their pre antibiotics site.
Nick Jikomes 25:29
Or they basically consuming the wrong antibiotic, the wrong probiotic, and putting the wrong bacteria in there.
Maayan Levy 25:35
There was question, so I'm not a probiotics expert. But if you think about probiotics. So I think one of the main questions is, are you actually putting something that is live into you, and whether this, you know, bacteria that's supposed to be alive? If you bring them into your gut into, you know, an environment that already has theoretic will they manage to survive? In the face of antibiotics, the situation is a bit different because you deplete the existing microbiome and you make an you know, an empty or niche for probiotics to grow. Yeah, I'm not sure if I would, you know, every time I would take antibiotics, I would immediately take probiotics to bring back the good bugs, because I, I don't think there is a one, one recipe that fits all, my microbiome is different than yours. We, you know, we don't necessarily need the same bugs. I think that, you know, something that is a bit less aesthetic is fecal microbiome transplantations, and then you recolonize your own gut with a sample of, of store, basically, this was taken before you started taking antibiotics. So you bring back your own microbes. This is something that is done, you know, in a clinical setting, obviously, not something that can be recommended to individuals that
Nick Jikomes 27:08
I see. Now, if you, you know, sometimes people take, you know, fairly large doses of antibiotics because they get sick, and they have a particular use case for it. But also, you know, my understanding is we're probably all chronically exposed to some sort of background level of antibiotics more or less all the time, just from it sort of being so widely used in modern society. Is there any understanding of how different our microbiome composition is? Because of that sort of environmental feature? Do our microbiomes resemble? What they would look like if if we didn't have so much use of antibiotics?
Maayan Levy 27:51
So you're talking about environmental exposure to antibiotics? Yeah. That is coming, for example, for the meat that we consume? Yeah, I
Nick Jikomes 28:00
think it comes from the food supply. I think, you know, people even detect it and water like it's it's sort of, like this background level of antibiotics sort of everywhere, it seems.
Maayan Levy 28:11
So what question I am not aware of any studies that that specifically addresses this question. One way to test it in, at least in you know, in animal models would to expose them to a very, very low level on of antibiotics for a really long time, and then look at their microbes, I maybe it's if it's, you know, the dose is too low to cause microbial killing, but it is enough in order to enhance the growth of others. And now, okay, now, I will cancel this, I don't think I'm not sure if you would be able to answer this question.
Nick Jikomes 28:55
Got it. Got it. So let's say let's say someone takes, you know, a dose of antibiotics because they get sick. So they have a particular need to take the antibiotics they recover. In that window where the microbiome is depleted. Is there any increased susceptibility to different diseases developing in that window?
Maayan Levy 29:15
I would think that there is an increased susceptibility to other infections. So one of the main functions that that our microbiome is providing is colonization resistance. So by having this huge community in our guts, whenever there is a pathogen, it you know, the it's the first thing that this pathogenic bacteria would see. So they, they would compete on nutrients and space and when you deplete it, by using antibiotics, you basically free the niche. Now there is much higher availability of food and more space to grow. So where pathogenic bacteria can grow more, so I saw Yes, it's a It enhances the susceptibility increases the susceptibility to secondary infections.
Nick Jikomes 30:04
What about so there's this thing called the hygiene hypothesis? What? Can you explain what that is for people and just talk about? Like, is that? Do we think that there's good evidence for that? And what do you think that means?
Maayan Levy 30:20
So, yes, I think that the soda hygiene hypothesis is mainly linked to to allergy and diseases that we that it thought that we would normally not have if we would be exposed to bacteria, this theory says that, in, in modern society and our current lifestyle, we we, we are much cleaner, we are less exposed to bacteria. So we are less we are more prone later on in our life to develop allergies towards different components that otherwise we would have exposed, being exposed to earlier in life and develop and protective immune response against. Yeah, so it's, I think it's definitely true. I think that our you know, in our current lifestyle, we, we pay much more attention to hygiene, and definitely compared to, you know, hundreds of years back. This influences the development of the immune system and the possibilities to different diseases, including allergies later on, but not that I'm not in an allergy expert.
Nick Jikomes 31:32
But so the basic idea is, you know, the hygienic practices, we regularly engage in the modern world, you know, literally physically cleaning our bodies, wiping down surfaces using disinfectants using antibiotics, it's probably having some kind of affect the microbiome, and just the microbial world around us,
Maayan Levy 31:53
and our immune response as a result. I
Nick Jikomes 31:55
see. But you said there is good evidence that that is linked to potentially the development of asthma and allergies. Interesting. So what about what about like the subject of auto immunity as it relates to the microbiome? So I've gotten the impression from from looking at things that the microbiome is somehow connected to certain autoimmune diseases at least. And if Auto immunity is the state where the body is basically confused about cellular identity, and starts attacking its own healthy cells? How does this sort of detection and discernment mechanism of the immune system start to tie into the microbiome? And and when does it start to get confused and lead to autoimmunity?
Maayan Levy 32:43
So I think the question in autoimmune diseases is what exactly do you recognize? So you can if you think about the microbiome, as this additional organ that you have, you can even view different inflammatory diseases, like IBD is, is autoimmune diseases. And you can, in this case, you recognize, or you're, you have a problem in recognition of some microbial components. So this is one thing. The other thing is, is autoimmune diseases that that are driven by, by, by different components of our cells, and then they these kinds of cells will be attacked by our own immune response. So we will recognize them as something foreign, while we actually need to, to recognize them and self and not mount an immune response against them. So we're not immune diseases, the body is confused, are they immune, the immune system is confused, and it reacts when it shouldn't be reacting or towards something that it shouldn't recognize as foreign.
Nick Jikomes 33:57
So okay, so So what you're saying is kind of interesting. So in a case, like, let's just say type one diabetes, you know, your immune system starts attacking some cells in your pancreas, which are important for blood sugar regulation, and they get destroyed. And the result of that is diabetes. But just like the pancreas is an organ of our body, and it's, I mean, it literally is it's made of cells with our genome, you're saying that one way you might think about the microbiome is it's the population of bacteria that live in our gut and elsewhere, and even though they're, they're not us in the sense that they have a different genome. It's sort of like another organ, and we want to be unconfused about the identity of that in the context of the immune system so that we don't attack the good bacteria say, and, and so something something like that can happen. Yeah. Interesting. So what So what I mean are some of these things like IBD, and some of these gut health, autoimmune issues, my understanding is that they're getting more common over time, at least in the US, is that Is that true?
Maayan Levy 35:01
Yes, it's, it's true. I think that this is, you know, these kinds of diseases that are greatly influenced by our diet and lifestyle. And this is something that has changed over the last few decades, dramatically. You know, we, we eat different kinds of foods, we exercise less, we completely changed our lifestyles, and susceptibility to different diseases changed accordingly. You know, one, if you think about higher susceptibility for cancers in the GI tract, you can, if you look at the trajectory, you can clearly see that there is a very clear increase over the last few years. And, you know, I wouldn't think that, you know, our genomes did not change so rapidly. So it's something that we either the lifestyle, the change, or something in our lifestyle that affects the rate of acquiring new mutations that then increase the susceptibility to different intestinal cancers.
Nick Jikomes 36:18
I see so So something's going on, though, where in the gut certain diseases where whether it's something inflammatory, like IBD, or even cancers, as you just mentioned, are going up over time. So something's going on down there. I know that one of the things you've looked at recently had to do with colon cancer, and how it's influenced by certain certain aspects of diet. So can you describe what the basic the basic thing was that you studied there?
Maayan Levy 36:45
Sure. So I can tell you first why we even looked at colorectal cancer. So in, in most of the cases of colorectal cancer, but somewhere in two thirds of the cases, there is no known genetic mutation that is, you know, is driving these kinds of cancers. So we we think that, in contrast to a specific gene that is mutated, there are other factors, including environmental factors or lifestyle that can make us more or less susceptible to developing colorectal cancer. And if we're thinking about specifically, in the case of colorectal cancer, then one of these, these lifestyle factors that was associated to CRC development is diet. And in, in multiple studies, it was shown that different kinds of diets make us more likely to develop colorectal cancer. And these diets include diets that are very rich in in sugar, Western diet, and even consumption of red meat, and specifically proteins and proteins that come from from an animal source like red meat. But from from these kinds of studies, we basically know what we should avoid. We don't know if there is any specific diet that will protect and not make us more likely to develop cancer. So the project that you mentioned, started from this question of whether we can find a diet that will be protected from rectal cancer or even could be used as a treatment for colorectal cancer? Yeah, so this was the this was the beginning. And the main question that we had in mind.
Nick Jikomes 38:41
This is Yeah, it's really interesting to the idea of using diet or exploring diet as a potential treatment for certain diseases. And I want to dig into that. But why don't we start out by just describing for people, what is the diet that you looked at? And then what is the diet? Yeah, like, like you proposed.
Maayan Levy 38:58
So we, we work in a lab setting, so we could design diets that were matched in there. There are different components and other components, we could change. So we had controlled controls, and we could use that were specifically designed. So we designed six different diets. And these diets had constant 14 levels. And they only varied in their fat to carbohydrates ratio to the basically fit to sugar ratio. And what we found so we fed mice in six different diets. And then we induced colorectal cancer in a few different models. So we have in the lab the ability to, to make or to to have the mice develop colorectal cancer, and these mice were fed the six different diets. And then we looked at the consequences and what
Nick Jikomes 39:55
you can just you can just get like turn on colon cancer in certain mice. Yeah. Are
Maayan Levy 40:00
there other ways? Yeah, how does that work? So, there are a few ways to do it, you can you can induce colorectal cancer by using transgenic mice or mice that have mutations in tumor suppressor genes, and you can induce colorectal cancer by a more inflammatory mechanism by injection of a carcinogen and then inducing inflammation. So it will be an inflammation derives cancer. So, there are few ways they vary in their duration, and slightly the outcome, the size of the tumor. So, but at least in this particular project, we, we used all the available models that we had. So, it, it, the observation that we had could be verified across different models.
Nick Jikomes 40:57
So, what was there, so, you have the six different diets, all protein matched, they basically only differ in the ratio of carbs or sugar to fats. And you've got these different models of colon cancer, these different types of mice that are susceptible to colon cancer. So you induce cancer in these mice in each of the groups getting each of the different diets and what was what was the basic result.
Maayan Levy 41:22
So we, we could follow the mice at different time points, because we have in our lab, a mouse and the scope, so we can perform colonoscopies on these mice and, and follow the progression of tumors throughout the experiment. And what we found is that the mice that were fed the diet that were very rich in fat, and very low in carbohydrates, they hardly developed any tumors and the tumors that they did did develop or significantly smaller in size. And that if we just look at the fat content of the diet that we used, the fat, the percentage of fat varied between 0.3 all the way to 90% fat. And we found this protective effect in the diet that had 90% fat, and 99 090. Yeah, and these diets are called ketogenic diets, as I'm sure many, many people now know, it became a very popular diet over the last few years. And these ketogenic diets, they're very, very high in fat, and they are low in carbohydrates. They have enough fourteens and in calories in these kinds of diets for originally developed in the 1920s as a treatment for epilepsy. And specifically in kids that didn't respond to regular medications, they will put on a ketogenic diet, and in the majority of the cases, it significantly improved the outcome in these patients.
Nick Jikomes 43:03
So you find this interesting effect with tumors when you're having a ketogenic diet 90% Plus fat. You have this sort of anti tumor effect in mice, ketogenic diets used to treat epilepsy. So something interesting is going on what actually so when you're when you're consuming a genuine ketogenic diet, how do you how do you how do you know that physiologically, what's going on in the metabolic processes of the body that changes.
Maayan Levy 43:30
So ketogenic diets is called ketogenic because it induces the production of ketone bodies in our body, and ketone bodies are small. There are molecules that are derived from fat, and they provide energy to tissues when glucose is not available. So when you consume ketogenic diet, the level of glucose is really low, because we consume less sugars, and then different organs in our body including the brain, they, they need to get their energy somewhere. So, some of the of the, of the tissues in our body they cannot get enough energy by just metabolizing fat, they cannot metabolize fat, and they need to have this alternative source of of energy. And our bodies and specifically our liver can take these fats and bye bye, different mechanisms and oxidation processes, these fats can be converted and made into ketone bodies. And these ketone bodies can now go all the way to the brain and give the brain enough energy in in these cases where glucose is is not available. So these are very, these are compounds that are very energy rich, and they provide energy to these other places. When When glucose is not available,
Nick Jikomes 45:03
I see. So when when sugars not in abundance, the body needs to get energy from somewhere, that energy is stored up in this fat, but it's not, it sounds like it's not in like the best format for all the cells of the body. So the liver turns that some of the fat into ketone bodies and those ketone bodies then like go through the blood and get into the brain, and then they're used to run neurons and things like that.
Maayan Levy 45:25
Yes, they, you know, we cannot function without an, you know, an active brain. So, these ketone bodies are a way of, of getting the, the required energy to the, to the brain and to the periphery. It's basically an alternative source of source of, of energy.
Nick Jikomes 45:46
And this state, like when when you are doing this in creating these ketone bodies, that's what they call ketosis.
Maayan Levy 45:51
Exactly, yeah. And you can get to a state of ketosis, either by consuming a ketogenic diet, but you can also get to a stage of ketosis when you are fasting for long periods of times or starved starvation. And these, these ketone bodies are produced by fatty acids, better oxidation of fats that are coming from the phone,
Nick Jikomes 46:17
and how much does it matter? What kind of fat like does the keynote? Is it any kind of fat saturated, unsaturated polyunsaturated does does that stuff matter?
Maayan Levy 46:26
Yeah, so it doesn't matter. In the case of ketogenic diets. It's, it is recommended to consume mainly unsaturated fats, and less of the good fats like avocado and olive oil. But I think that the main point here is not really what kinds of fats you consume, but how much carbohydrates you bring into the system. So it's mainly the the low glucose levels that that drive the formation of ketone bodies.
Nick Jikomes 47:02
I see. I see. So it's a high fat diet, maybe it doesn't matter so much. What is critical is that it's low, low sugar, low carb. Exactly. And what how did the how to how much does like protein matter? Like, could you go into a state of ketosis if you were having a high fat, high protein diet that had low carbs?
Maayan Levy 47:20
No, I think this is the diet, it is called the Atkins diet. It has, it's a different kind of diet that was designed in the 70s for weight loss. And this diet also has restriction of carbohydrates, but it doesn't restrict proteins or calories in general. So in this kind of diet, you will not go to a state of ketosis so quickly. So the the main key here is to give a lot of fat limit protein consumption and reduce carbohydrate consumption. So that if you look at the fat content in relation to carbohydrate, it's the traditional ketogenic diet is called Four to one from a ratio. So you will get 90% of your calories from fat 8% from proteins and only 2% from carbohydrates.
Nick Jikomes 48:17
I see. And so if you have too much protein, even if you're doing a high fat, low carb, you won't go into ketosis is that because the proteins are getting used to make something other than keto ketone bodies?
Maayan Levy 48:28
Yes. Yes, you can break for things to make energy it will be a parallel process. And in when when you consume ketogenic diet it is that has limited amount of protein, the major source of energy is fat will come from fat in Yeah. And how
Nick Jikomes 48:49
fast is this process? So let's, let's say that you're eating a traditional Western diet today. And then you know, you listen to this podcast and you're like, alright, tomorrow, I'm gonna go on the ketogenic diet, how long will it take your body to make that switch and go into ketosis? Just few days, a few days. And do people like obviously, you can measure it physiologically? It has effects in the brain that maybe we'll talk about in a little bit. Can you do people report that they feel different?
Maayan Levy 49:17
Yeah, so I, personally, I haven't tried going on a ketogenic diet. I think it's it's a major commitment to make. But from what I saw, you deprive your, your body from sugar, and I think we're all to some level addicted to sugar. So I assume that the first few days are more challenging, you're more tired. I saw that people report, headache and nausea and generally feeling like flu like symptoms, but then your body gets used to it and and then you know, you don't suffer from the symptoms anymore. And
Nick Jikomes 49:58
it sounds like drug withdrawal. Oh, yeah,
Maayan Levy 50:01
it's I think it's really it's like a sugar withdrawal. That's
Nick Jikomes 50:07
interesting. Okay. So anyway, let's go. Let's go back to your study. So So now we know what ketosis is. We know what the ketogenic diet looks like, you gave these mice this ketogenic diet, high fat, low carb, not so high protein. It had this anti tumor effect. What What else did you find? I know, there's some more some more detail there.
Maayan Levy 50:27
Yeah, so maybe before we should we, we go into more details in this study, which I think we should mention that ketogenic diet was tried already in the past, by, you know, many, many different groups in different kinds of cancer therapy, different kinds of, of tumor models. And it was shown that in some cases, it is beneficial. But in in other studies, it was actually shown to have an opposite result. And in in other cases, it was shown to have absolutely no effect. So I think that ketogenic diet can be beneficial to for specific cancer types, but not others. So the different the effects can be different. And I think that the other point that was made by by other studies is that for every, every patient might have different mutations, even if the cancer falls under the same category. So it's not necessary that, you know, the, the one patient will react in a way that will be identical to another patient. So you need to take into account the different genetic alterations and in two more associated syndromes between different individuals. But what we found in our study is that so this ketogenic diet is protective. And we asked ourselves, how can a ketogenic diet be protective in colorectal cancer. And we already mentioned that ketogenic diet is inducing the production of ketone bodies in our liver. And these ketone bodies are beta hydroxybutyrate, acetyl, acetate, and acetone. And beta hydroxybutyrate, or bhp is the main ketone body. And this is actually also the main source of this alternative energy. So we, we try, we ask ourselves whether one of these ketone bodies is mediating the protective effects of a ketogenic diet. And in order to do so we had two parallel approaches. One is to give mice, these ketone bodies to these mice were fed a normal diet, the diet that that mice are fed regularly. And they were given BHB on top of these regular diets. So they they didn't go on a ketogenic diet, it's on just
Nick Jikomes 53:03
orally, yeah,
Maayan Levy 53:04
you can consume it orally, you can give it in the drinking water, you can, you can buy it in a form of of a drink in the form of different oils, it's available. It's it's not a drug, it's a supplement. So it's something that that is very easy to obtain. And we found that it was enough to give mice BHB this ketone body in order to prevent and treat existing tumors. We
Nick Jikomes 53:34
so you recapitulated the results from before just by giving them BHB even though they were having a regular diet with carbs in it.
Maayan Levy 53:41
Exactly. Yeah. So as long as you you elevate the levels of BHB either by ketogenic diet feeding or by giving BHB exogenously from outside, you can have the same beneficial effect. We saw that in so we did this these kinds of experiments in mice, we also had, we also use the really cold system, which basically allows us to generate mini guts meaning test times in the lab. So we can take small pieces of of the of the Gatto of a mouse or of a human patient. And under tightly regulated conditions, we can force these small pieces of tissue to form 3d structure that resemble the the intestinal epithelium, and we can treat this mini guts in culture in the lab with beta hydroxybutyrate and see a similar response. So in mice when we induce tumors BHB treatment leads to protection and the mice that are traded with BHB develop less tomorrow. And when we take this page when we give it to these small mini guts, these these, these 3d stuff features they proliferate less, so they are smaller in size. This is also something that is beneficial if you're thinking about cancer development, you suppress cellular proliferation.
Nick Jikomes 55:10
So so as BHB, directly modulating some critical part of the cell cycle.
Maayan Levy 55:18
So what BHB is a molecule that is studied extensively. But what we found is that the beneficial effect of BHB is mediated by the receptor of BHB, that is called GPR 109, a or H car. And after BHB binds to its receptor, something is happening inside the cell and it leads to reduced proliferation. What we identified is that downstream to this VHB, H car and cellular between this until our profession there is another gene. And this gene is called Hope, x. And this gene was previously suggested to be a tumor suppressor in different kinds of cancers. So, we found that, by giving BHB to mice or to intestinal organoids, these mini guts, we can induce the levels of these tumor suppressor hope x. And this is enough to, to protect so when you have when you treat with BHB, or with ketogenic diet, if you give it to hope to mice that don't have hope, x or x deficient mice, they are not protected anymore. So in order to have the protective effect, we have to have GPR, one on line a the receptor for BHB and also have X
Nick Jikomes 56:41
I see. So BHB levels go up, either because you take it as a supplement, or because you go into ketosis because of the ketogenic diet, or because you're fasting or something like that. The BHB is going to be sensed by receptors in cells of the gut. And then stuff happens to the genome genes turn on genes turn off. And the net result of that is basically less cell division.
Maayan Levy 57:05
Exactly, yep, the cells proliferate less. And if you think about a tumor in the gut, and the cells proliferate less, less than you, the outcome would be smaller tumor, so the tumors will be smaller in size.
Nick Jikomes 57:21
Interesting. And so, I mean, so you literally said, so BHB, it's, it's a, it's a ketone body, it's can be used to make energy, obviously, you can give it to the mice as a supplement. Is this also a human supplement? Like, can you go to the store and buy a bottle of BHB? Yeah,
Maayan Levy 57:36
you can buy it on Amazon.
Nick Jikomes 57:39
So then you just take it as a health supplement, but your study just came out. So why was it what do people use it for already?
Maayan Levy 57:46
So people use it for for different kinds of reasons. So, it has this you know, the people see it as something that is overall healthy. But b2b is is is used for treatment of different different diseases, such as different metabolic diseases. I saw that that people take it for for acne, different different neurological disorders such as Alzheimer's, Parkinson's.
Nick Jikomes 58:33
I mean, in the world of health supplements and health claims, you know, generally I would be skeptical here. But but, you know, we I do want to talk about the effects of the ketogenic diet, and BHB on epilepsy because you mentioned it before, and I know that there's some pretty dramatic effects there. So can you summarize what that is for people and what's going on in the nervous system?
Maayan Levy 58:56
Yeah, so I think that's it's not completely clear the mechanism of action of BHB and I think that this is something that we're lacking, especially in the field of dietary supplements. But so in the case of epilepsy, it was shown that so that people got to the, to the this observation that that ketogenic diet is, is protective, because when, when kids were put on some kind of starvation protocol, they found that they these kids developed or they had less seizures, and then they they tried to design a diet that will mimic this fasting. And they found that ketone bodies was one of the of the parameters in the blood of these kids that was different. It is thought that that it can be beneficial in the case of epilepsy, through different mechanisms. It can change the the the On the stimulation of nerves, the and how the excitation of nerves and the the abundance of neurotransmitters so it can suppress the or reduce the amount of neurotransmitter. So this is one idea. And the other idea is that if you give BHB a ketogenic diet, you may make the state that was in the developing brain. So by by by creating an environment that is more similar to a developing brain environment, you will basically enhances or promote the recovery of neurons. I think these are the main two, two suggested mechanisms. One is the effect on neurotransmitters and an activity of neurons and the other one is repair.
Nick Jikomes 1:00:59
I see so so a lot of the details are still mysterious, but BHB is having dramatic effects in the brain in terms of cellular neurophysiology, and it seems to be generally the case that when you're in a state of ketosis, or BHB levels are high, that the sort of the the environment of the brain is a little bit more like the developing brain is conducive to new neural growth, which is basically the opposite of neuro degeneration.
Maayan Levy 1:01:27
Okay. Yeah. Interesting, but I'm not a brand expert.
Nick Jikomes 1:01:33
What about what about effects on like immune responses and autoimmunity? Is there any known interaction between ketosis and that?
Maayan Levy 1:01:42
Yeah, so actually, when we, when we did our study, we, we didn't know that, or at the point where we only had the observation that ketogenic diet is protective. We asked ourselves, how can a ketogenic diet be protective in the case of colorectal cancer, and there has been several evidence by now that it can affect the immune response by different mechanisms. One is by inhibiting one of these inflammasomes inflammasome complexes that is called NLRB three inflammasome. So BHB, and ketogenic diet was shown to inhibit this innate platform of the NLRB three inflammasome. It was also shown that his genic diet consumption changes the composition of the microbiome. And this leads to different abundances of immune cells, and as a consequence, different immune responses. But we saw that even though we could observe similar, similar, similar results in in our system, so also, when we feed my Skeeter genic diet, they have less inflammatory cytokines. So the NLRB three is in front of them is important, but it doesn't mediate the protection effect in the case of colorectal cancer. So if you take NRP, three knockout mice and wild type mice, and you treat both of them with ketogenic diet, and you look at the cancer development, the knockout mice in the wild right mice will both be protected protected when they affect ketogenic diet. So NLRB three might be affected by ketogenic diet, but it's not driving the protection in the case of colorectal cancer. It has many different and other important functions, but not in mediating a protection from CRC in mice. The same is true for TNB cells, we use mice that don't have any of these adaptive immune cells. And also their ketogenic diet was protective. So even though these mice are deficient in a very major part of their immune response, or immune system, then even though they don't have this part, they can still have the protection that is mediated by ketogenic diet or by toxic water. And so ketogenic diet can change many, many different many different aspects of our physiology. But it's not these all these different parameters do not necessarily drive the protection.
Nick Jikomes 1:04:17
You know, so far, the ketogenic diet is very popular right now. I mean, a lot of people have at least heard of it. A lot of people have tried it. So far in our conversation, we've talked about only good things, right? Like ketogenic diet can have this anti cancer effects sometimes, although sometimes you did say it is possible to have the opposite. Yeah, it has this anti epilepsy effect. Is there. Are there any downsides here? Is there any reason? You know, everyone shouldn't just go buy a bottle of BHB and start consuming it?
Maayan Levy 1:04:43
So I think we should make the distinction between ketogenic diet and BHB. So, I think that ketogenic diet was shown to be beneficial or not beneficial, depending on on the type of cancer and the context It was even shown to enhance the efficiency of other kinds of cancer therapies, it was shown that ketogenic diet can enhance the efficacy of targeted therapies. If I remember correctly, the big three kinase inhibitors if you give a ketogenic diet, when you treat with these kinds of inhibitors, you will make the treatment more effective, it improves the efficacy of the classic cancer therapies. In some cases, this these kinds of diets, they're very, very rich in fat. So you would think that they will induce elevated cholesterol or, you know, negative negative consequences on our general metabolic health. But it was actually shown that it doesn't, it doesn't really, it doesn't greatly change the body composition or the different parameters in our blood. And, as far as I know, no studies reported any severe adverse effects of ketogenic diets. So it's, as far as I'm aware, it doesn't cause any deterioration of metabolic markers, not cholesterol, no, not triglycerides.
Nick Jikomes 1:06:27
And what about, what about BHB? supplementation? Is there any reason to be cautious about that?
Maayan Levy 1:06:35
I'm not a physician. So I cannot say if it you know, if there are certain conditions where BHB should not be taken. I think that if you can prepare just BHB supplements, and you compare it to a whole ketogenic diet, I think that in terms of you know how practical it is, I think that drinking a BHB supplement is, is much easier than then adhering to this very, very strict diet that doesn't have any carbs, and basically limit it's almost an antisocial kind of diet, because you cannot go out you cannot have alcohol, you cannot, you know. So, I think that just drinking age be something that is is is more realistic. I am not aware of any negative side effects of consumption of BHB, or these ketone supplements. I saw that, you know, some of these supplements, they can cause some discomfort in the gastrointestinal tract. But this is something that usually goes away. I think after a few days, not all supplements taste good. But other than this, I'm not to have any major side effects.
Nick Jikomes 1:07:51
Yeah. And I would imagine, too, there's, there's feedback here, like if you go into a state of ketosis for a prolonged period of time, is that well, so if you were to take if you gave if you gave mice or humans, but maybe you've done this in mice, if you give them BHB supplementation, but not before ketogenic diet, so their their diet doesn't change, except that they've got this BHB supplementation. Does that cause is that sufficient to cause clear changes in the microbiome composition?
Maayan Levy 1:08:22
So, because the genic diet definitely alters microbial composition? In the case of BHB, it's less clear. I
not sure we even looked at it, you know, I Yes. But I would think that, yes, just because we can change our innate immune system, which then can modify and affect the composition of our microbiome. So my guess is yes, it will change.
Nick Jikomes 1:09:00
The other thing I want to ask about is, so obviously, our bodies have the capability of switching into these different metabolic states, ketosis. And then I mean, I'm sure there's multiple other ones that I don't even know about. But the fact is, we can do it. And if you think about, you know, think about this in evolutionary terms. You know, if you think about wild animals, or human hunter gatherers, you know, present day or in the past, they probably generally lived in environments that were much less stable and plentiful dinars in terms of food availability, so they had to go through periods of feast and famine, sometimes food was abundant, and sometimes it was scarce, and you didn't have a choice as to whether or not you're going to be fasting, it was just sort of a part of the natural cycles of life. So I mean, with that in mind, when we think about sort of the the natural human ecology that our bodies evolved under our bodies, sort of like expecting to switch metabolic states at different times and not always be in sort of like one on diet one mode of metabolism?
Maayan Levy 1:10:03
Yes, I think, you know, it's exactly what you're saying, We, our body has to have this backup, in case we will, you know, will encounter a long period of of starvation or when when food will be less available to us. We can, we can, you know, lose weight, but our brains, they, you know, our brain has to have enough energy in order to continue function. And it's not just our brain, it's other organs like, like the heart and our muscles, they not all these peripheral organs can can get enough energy in the absence of glucose, just by consumption of fat they need they are relying on this, they rely on these ketone bodies to to get to them and to allow them to get enough energy. Yeah, so it's definitely you know, it's something that is very important from an evolutionary point of view. Because, you know, in the past for the availability was much less predictable.
Nick Jikomes 1:11:10
What, what are some of the things? What are some of the big questions that you guys are working on in the lab now?
Maayan Levy 1:11:17
So I think that in at least in the case of the ketogenic diet, or BHB story, there are a few, few next interesting questions. One is whether the microbiome is playing any role in this protection is something that we're currently addressing, so I cannot comment about it at the moment, hopefully soon. The other question is whether you can combine BHB with existing treatments for for different kinds of cancer. So we identified one specific mechanism by which ketogenic diet is protective. In the case of colorectal cancer, I think that it will be interesting to get to this kind of mechanistic understanding of the effect of ketogenic diet or better Doxie Boatright. In other cancers. We talk most of the work that we that we've done and the two are currently working on in my lab is based on animal models of of cancer. We have some evidence that is also included in the paper that was recently published that suggests that a similar phenomenon can also be observed in in humans. So we found that in colorectal cancer patients, the amount of BHB correlates with these, these different genes that were identified, specifically hope x. So when patients have higher BHB, they have higher levels of hope, x. And they also have reduced cellular proliferation. We found it by single cell RNA sequencing. And yeah,
Nick Jikomes 1:12:57
I'm just gonna say this. Yeah, I mean, this is this is a really interesting finding just beyond beyond your specific results for colon cancer and the ketogenic diet, because it's sort of, at least to me, it's saying, well, if one of the main cellular, physiological effects here is to limit cell proliferation, it's very natural to suspect that this isn't going to be limited to the colon. And it's also starts to get you thinking about like, Okay, if, if the Western diet in the western lifestyle is having this sort of pro cell proliferation effect, it starts to point to a story where like, yeah, maybe maybe that's exactly why a number of cancers are on the rise and associated with this kind of general lifestyle.
Maayan Levy 1:13:37
Yeah, I think that's. So we identify the specific pathway of ketogenic diet BHB and how it acts inside the cell. I wonder if in order to observe a similar protection in other cancers, or even, you know, in other organs or in different cancers along the GI tract? Would you need to have the same cellular machinery in order to have the protection or let's say, you will now observe a protection in, you know, in cancer in a completely different organ? Do you need to have the same receptor the same protective genes in a way in order to have protection or are other genes important in different cells? So I think that the mechanism can be different between cell types between different types of cancer. This is a really interesting question. A, we currently are in the process of of starting clinical trials in in colorectal cancer patients. So we will treat patients with BHB and we will see if we can observe something similar if we see this protection also in in humans that are treated with BHB and not just in mice to this. This is something that is current play an active, ongoing clinical trial that hopefully we can get first results from in the next couple of month.
Nick Jikomes 1:15:07
How much? How much BHB do you give to patients?
Maayan Levy 1:15:10
So we gave the recommended amount the patients will drink BHB drink three times a day. And it's it's a relatively small volume of approximately 30 mils 30 milliliters.
Nick Jikomes 1:15:27
Yeah, so it's not like a mega dose or something. It's a normal amount. Yeah, yep. Interesting. Well, this is fascinating stuff. I mean, I think this is an interesting area, just the general, you know, the general idea that diet can have such a physiologically potent, potent effect on us at the level of, you know, preventing disease and things that maybe we don't haven't appreciated historically, as much as as much as we are starting to. So I'm definitely looking forward to see seeing what else comes out of out of this work from your lab.
Maayan Levy 1:15:58
Thanks. I think it's really I think it's really exciting. And I think that it will be really interesting to see if we can design diets that will be protective or prevent different kinds of cancers, different kinds of diseases, understanding, you know, what is the mechanism of protection in case we identify such and whether we can design diets that will support existing therapies, the the therapies, at least in the case of colorectal cancer these days, have major side effects chemotherapy and surgery, if you could maybe, you know, give patients BHB and you know, reduce the chemotherapy or you know, change the the amount of chemotherapy they would need to take you would improve their quality of life significantly. So, I think there is a lot of potential of treating with BHB or even other molecules that can be identified that are coming from diet or that are influenced by diet either as standalone therapies or in combination of, of existing standard therapies. And it's again, it's not limited just to to BHB it can you know, the same kind of studies can be performed with different diseases, different diets, different molecules, which be different microbial metabolites I think they're the possibilities here are endless.
Nick Jikomes 1:17:25
Well, I think that's a great spot to end it doctor man love you. Thank you for your time.
Maayan Levy 1:17:31
Thank you so much. Pleasure.
Unknown Speaker 1:17:33
Morning
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