Brian S. Kim MD, MTR, presented virtually as a keynote speaker, “Neuroimmune Regulation of Itch” to the Anesthesiology Branch of the Chinese Geriatric Society 2022 Annual Meeting in August, 2022. How does the healthy skin barrier become inflamed? How does inflammation within the skin lead to neurophysiologic pathology? Dr. Kim views the skin as a model barrier paradigm in which to understand other organs and various surfaces and to understand neurophysiology and sensation more broadly. Dr. Kim discussed atopic dermatitis as a model disease and presented a deep dive into his research in itch biology, leading to successful new therapeutics.
Thank you, Professor Wong for the invitation. Thank you to the organizing committee. It's a great honor to be presenting here today. So uh in the interest of time, I will move swiftly through the presentation here here are my various disclosures. So the first question that I'd like to address is how does the skin sense itch? And it's a it's a very simple and fundamental question. And the way in which I consider this is actually as a physician. When we think about the peripheral nervous system, we break it down into two simple components, which is the autonomic nervous system which we know through Colin ergic and adrianne ergic input regulates a whole host of physiology and organs like the lung with regulating the airway, broncho constriction and motility in the gut heart rate in the skin. This aspect of the immune system. The nervous system regulates primarily processes such as sweating and and vascular tone. But what I'll be talking about almost entirely here is the somatic sensory nervous system which is what relays signals from the environment back to the brain. And essentially gives us a way to kind of sense the outside world. And there are various in very simple terms. There are various different nerve fibers such as a beta fibers which can actually sense mechanical sensations such as the hair follicle moving, or the hair shaft, a delta fibers which also uh sense mechanical stimulation in some form of pain. And then you have the UNM I eliminated polymetal C fibers which sends everything from pain, heat, cold and even itch. And I'll be talking primarily about which here today. So what do we know about it? Well, it has been one of the most overlooked sensations in terms of the biology as well as medical practice at least in the United States uh for a very, very long time. And in large part because there was a lot of misunderstanding about what it is, it was often viewed as a mild form of pain and many believe that if we simply understood pain better that we would actually solve it. But some seminal discoveries, I would say I'm going not necessarily from left to right in terms of uh in terms of temporal sequence but it really started with in the spinal cord. The discovery of Gaston releasing peptide receptor positive neurons in the spinal cord by ju fang Chen which was a very big discovery and um in fact this is the first author here is a young gang son who is in china and a very prominent researcher has also identified that there are areas within the brain that sense which such as the prayer breaking nuclei. But then if we go back into the skin and what is it that what what sensory neurons actually sense, which we know that there are for instance sensory neurons that sense it by way of mass related g protein coupled receptors discovered by shin dong dong and then Mark owns group has identified for instance neuro peptides that come from the sensory neurons such as brain natural peptide that activate neurons in the spinal cord and this this whole circuit goes up to the brain and from the skin all the way to the brain we sense which um what these discoveries have done is allowed us to actually understand it as a uh sensation that is distinct from pain that it is truly a specific sensation and this is really uh emboldened both research as well as clinical therapeutic investigation with regard to itch, I'm actually not a neuroscientist, somebody immunologist. So what we've been focused on prior to entering it sure was really understanding how does the healthy skin barrier become inflamed and then more recently, understanding how inflammation within the skin leads to neuro physiologic pathology manifesting its edge. Two points I want to make is that we, although I am a dermatologist, I I view the skin as a model barrier paradigm in which to understand other organs and barrier surfaces and we use it as a model paradigm to understand neuro physiologic peripheral neurophysiology and sensation more broadly, we used a topic dermatitis as a model disease or eczema which is very common. Many of you in the audience will recognize this if not know someone who has it or may even have it as well and we know that this is a was a great disease in which is study inflammation in it because it is a chronic inflammatory disorder that is a defining feature is not just a rash but also the component itself as well. When we first embarked on these studies, it was actually understood that there are certain kinds of stimuli or allergens in the environment that cross the skin barrier and activate this adaptive immune cell. The T. Helper type two cell which has antigen specificity to this day. What exactly does to drive this kind of inventory process that remains unclear. Notwithstanding this, we know that the cytokines that were produced by these uh this this th two cell elaborate a whole host of other pathologies such as the production of antigen specific i. G. E. Defining feature of a topic disease as well as the cytokines can directly actually damage the barrier itself. My own work during my postdoctoral fellowship was informed by the discovery of epithelial cell derives alarm inside of these cytokines actually do operate as alarm signals because upon damage to the various decided kinds were already known at that time to activate broadly this pathway. When we look downstream of this pathway, we actually identified entirely unrecognized contributions at that time of rare circulating Besa fills as being major sources of about four as well as entirely undiscovered at that time. Group two innate lymphoid cells or I'll see to is in the skin is being major sources. About five and 13. We now know that decided kinds are critically important, particularly of four and 13 in the pathogenesis of a topic, dermatitis and other allergic disorders And this is therapeutically validated now, but when I first started my laboratory, a key discovery that we made was we identified that canonical side type two sided kind such as ill for 9 13 can directly stimulate the sensory nervous system by way of their cognitive receptor out for receptor alpha, additionally downstream of the cytokine signaling pathways exquisitely dependent on Janice, Kinney's particularly Janice dinosaur Jack one signaling within the sensory nervous system, some components that were largely ascribed to the immune system. We were now discovering to be very important within the sensory nervous system and just to highlight some of the work. This is work by my first uh M. D. PhD graduate student Landon, who's now a neurology resident at Harvard Medical School, identified by simply extracting sensory dorsal root ganglia that in fact there is expression of for instance, canonical type two cytokine receptor, alpha receptor alpha as well as even the native aisle 13 receptor alpha one. And we were using at that time the known pretty jin receptor component, I'll 31 receptor as a positive control. And what we found was in fact the expression of these cytokine receptors were not only present but also conserved between mouse and humans. And this largely remains a durable feature of both. Type two inflammation as well as its which we believe is now an extension of type two inflammation is a very ancient and highly conserved through across many species um uh modules within both the immune nervous systems. We then showed that in fact not only are these receptor components expressed within the nervous system but by using calcium imaging approaches which detect calcium influx into the sensory neuron. We can then stimulate these sensory neurons from both mouse and human dorsal root ganglia. With comment, I'll form within a matter of a couple of minutes. We can detect calcium spikes in the indicative of activation these neurons. And here we see with human I'll for that this neuron itself is capsaicin responsive, indicating this is a tricky one positive neuron. So the question then for us is how do we validate pre clinically that this is in fact important in terms of disease phenotype. Swee use mouse models to do this. We use a validated mouse model in which mice are treated either with vehicle control or compound M. C. 903, which is a vitamin D analog that very reliably induces a topic dermatitis like disease and mice clinically histological e theologically If we look in this mouse model in terms of RNA transcription profiling within the skin, what we find is that there is in fact up regulation of key type two pathogenic cytokines such as I have for all 13 as well as uh type two sided promoting alarm inside as I mentioned already like 33 into slp and a whole host of other factors that have been actually reported to be up regulated in human a topic dermatitis. If we look at the behavioral outcome of scratching in these mice, we find that with scratching bouts on the Y axis over time and days on the X axis, we find that these mice are chronically spontaneously itchy, very robustly. So when we induce a D. Like disease and to give an example of an approach, what we could actually do is then selectively delete file, Forest sector alpha just in peripheral sensory neurons by driving expression of career accommodates by way of sodium channel 1.8, which is very to the peripheral sensory neuronal compartment. So despite the fact that I'll Forest Sector alpha is widely expressed throughout many, many tissues and the immune system selective relation just within the peripheral sensory nervous system results in uh actually reduction in terms of scratching bouts as well as associated reduction in terms of skin thickness as well as you can see very grossly even hissed, a pathologically very dramatic reduction in terms of the inflammatory environment. What's interesting is that we saw a very dramatic reduction in terms of the pathology, which is something I will point out here in a second, is slightly different. When we look actually at some of the downstream signaling pathways, we now know that the blockade of this receptor is very, very effective in terms of mitigating edge in a topic dermatitis. And furthermore, when we actually looked at this time at single cell RNA sequencing data sets from uh the Karolinska Institute Patrick rainforest group. What we found is that What was being actually emerging at this time around 2015 is that there in fact our modules of its specific neurons within the peripheral nervous system that are poised to respond to very specific predictions. Origin using molecules. But what we observed early on is that selectively but also broadly across these itch sensory neuronal subsets that they had the capacity to respond to the type two sided kinds very broadly. Why why is it important that they were broadly expressed? We actually this then provoked the hypothesis that other itch conditions that are actually much more neurogenesis in origins and just Perego Nigel Harris a topic dermatitis is we conceived as a very inflammatory disorder that results in secondary itch but private actually this is a much more neurogenesis which condition that results secondarily due to scratching in these kind of hyper carry topic inflammatory nodules. We suspected that perhaps this would actually be an effective approach to block this pathway at the neuronal level that extends beyond even a topic dermatitis. And in fact we propose this to regenerate corporation here in in the new york area which developed the drug people. Um um and in fact This led to directive a street clinical trials which were reported out in October of 2020.1 with very positive results in salaries this drug in the United States is likely to be approved by the end of this year. So this means a new drug, the first FADA approved drug hopefully for this condition that it was a highly unmet need. We've also targeted patients with chronic peratis of unknown origin with a pillow map as well. For similar reasons. This was work that was led by john john supported by Fang wang, who's at the first affiliated hospital in china. And the interesting about these individuals, this is in line with the theme of geriatric medicine is that these are generally elderly individuals who develop it later in life. They generally don't have any history of a topic dermatitis or any allergic disorder. Really these individuals have scratch marks where they itch and can can reach they spare errors where they can't scratch. So this is not a primary inflammatory disorder. This is a truly itch disorder. And what we found anecdotally these patients do improve when treated with papilloma blocking dial for receptor alpha. If you look in from just our clinic over 30 months retrospectively in patients who have severe itch which is an n. r. score seven or greater 10 being the worst imaginable, which we found that all of these patients actually improved with off label use of the pill. Ahmad some quite dramatically. Um the question then is is this should clinical trials be directed with this drug towards chronic price of unknown origin we believe So and this where fortunately has seen that this clinical trial is now has been recruiting since March. We'll see within the next year what what it does. We are very hopeful and optimistic but downstream of the cytokine signaling pathways, we also appreciate the fact that these cytokines have to signal whether it's aisle 4 13 or 31 have to signal through the Janice, Kinison stat signaling pathways, at least in part even within the nervous system. We look at the single cell RNA sequencing data sets. We find that in fact Jack one particularly is very much enriched within these itch neuronal clusters. And if we look at recent work from steve Davidson's group, what we find is that these, its specific neurons that were identified by single cell RNA sequencing in mice or thala grisly are represented also in humans. So if you look there are at least two subsets of its specific neurons. In humans they express dial 31 receptor, they express the histamine one receptor, they express the brain metastatic peptide MPP B. B. But what you find is that there are at least two different clusters and this cluster in particular is highly enriched for Jack. One consistent what we have found in mice. And in fact, we if we actually conditionally delete Jack one just in peripheral sensory neurons, we actually find that these might actually exhibit very little effect in terms of the overall skin pathology into the skin thickness. So this is in slight contrast to when we conditionally delete the I'll force subject Alpha Jack one is the downstream blocks many, many other side of kinds. So there may be some other effects going on here, which I'll speak to in a bit but not withstanding this. If you look at the scratching bouts, we greatly reduce this when we delete Jack one just within the peripheral sensory nervous system. So one prediction that we made was that Jak inhibitors would be much more potent because they can actually inhibit you see Jack one and yellow blocking so many different kinds of factors we predicted. What this would result in is that these Jack him bitters especially Jack one inhibitors would be potent, rapid and broad in terms of their effect. And in fact if we look at clinical trials where Jak one selective inhibitor of babysitting, it goes direct comparator to diplomat now against the ill forest sector Alpha. What we find is that in fact is a much more dramatic reduction in which that actually outpaces and out beats out diplomat, as we had predicted. If we look with the other Jak one selective inhibitor, aber sittin in what we find in Orange here is the the high doses of adversity you get a very rapid improvement in terms of the edge that beats out Green Hill amount here as well. Um we actually early on when we discovered this kind of neuronal Jack one signaling, we had actually proposed a clinical trial uh and and and design a clinical trial. Phase two pivotal clinical trial with Incyte Corporation with the JAK 12 inhibitor, topical Rock Solid net which is now approved in the United States and readily available for our patients. But we've also used other Jak inhibitors such as Tofas Sydney, which is not a Jak one selective hitter, but a pan Jak jak 12, Jak three inhibitor. Uh And these patients with chronic peratis of unknown origin again do quite well. We find anecdotally in terms of itch. So what's going on here? So we think that Jack one is very very important for itch, that cytokine signaling within the sensory neuron is a very very important mediator rich. But we also believe that other cytokines and that even Jack signaling may actually regulate um not just itch, but also a neuro inflammation. So there are some side of kinds that may simply mediate itch and that's it and that's the end of the story but there are other side of kinds or or even disruption of Jackson and pathways that may actually interfere with the release of neuro peptides from these sensory neurons. So there is a both a sensory as well as an different uh neuro modular Torrey function and I think you're wrong g will be giving a talk later on neuro inflammation. So we think it's more than just sensation. There's also some aspects of neuro inflammation that may be impacted. And that's perhaps why we're seeing a discrepancy between the neuronal solution of our forest sector alpha versus neuronal regulation of Jack One. What we think is that cytokine blockade is not only anti inflammatory or jak inhibition is not just anti inflammatory but we believe some of these agents are in fact truly neuromodulation Torey in terms of their mechanism of action. Um And in the interest of time I won't be able to get into a lot of this data but there's more than what happens with chronic inflammation that there's chronic itch which is what I've been talking about all along. But we we appreciate as that knee topic dermatitis has been well appreciated for decades that chronic inflammation actually resulted in activation of Besa fills in and hyper I. G. Reactivity as these basic skills actually harbor high affinity receptor for I. G. What we found recently this is work from dr fang wang again at the first affiliated hospital that these basic tools are actually able to respond to environmental allergens. And this results in the production of the good try and C. Four which actually is a very very potent parity gin and activates which so despite the fact that this phenomenon of basic activation was known, it was not linked to itch until her recent work um what we do know based on work from Mark Hoon's group as well as Isaac choose group is that the receptor for Luca try and see for CSL tR two is in fact a very potent itch receptor. Uh and so we think that given the work from others in conjunction with ours, this really emboldens us to believe that this is actually very important pathway. Um And and in fact uh this is something that we are are interrogating more. But also the question here is in terms of the pacific biology um uh extending beyond uh even look to see for if we actually think about basic skills and how they are regulated we're starting to appreciate is that there are receptors that are very mass self specific such as M R G P R B two. But there is actually another receptor called MRG PR A six that we have found in collaboration with group is very very specific for the blood besa fill. So we actually believe that M R G P R A six is the mouse uh specific receptor for the blood basis. Fell while MRG P R B two is specific for mass cells, particularly uh these connective tissue mass cells, what's interesting about this is that while if we take for instance MRG Pr A six reporter mice and look in the blood that these these cells are essentially entirely basal cells, they are not mass cells. So they're seeking negative, they're not S NFL's. So cyclic negative. But what's interesting if you actually go from mouse to human, if we look at the M r G p R X two population which is the Ortho log of M R G P R. B two, what we find is that this population is entirely Besa fills in the blood. So M R G P R X two is a mass cell marker in the tissue. But Mark's Besa fills in the blood in my star to receptors the GpR B two and M R G P R A six which are respectively on mast cells and also to receptors for each cell mouse one consolidated in humans. This is a very controversial topic but we believe this is biology is very real. Um But if I bring this back to Not just the regulation of Besa fills but the fact that these basic skills are highly enriched for the production of Luca, try and see for a potent precision CSL tr to the receptor for Luca tree in C4 is on the sensory nervous system. What we find if we now go back to the single cell RNA sequencing datasets. If you now look these it's specific neurons within humans. Uh These two clusters here which are positive for L. 31 are a also positive for the co receptor uncle Settin em receptor and the brain naturalistic peptide as I mentioned earlier. NPP B is enriched within these clusters. What we find is that CSL TR two is also very much enriched within these clusters. So we think that this L. T. R two is a really good marker but also a functional receptor for itch that's very important for human uh h as well. So for the last part I just want to emphasize if we go beyond classical parroted and so not just molecules that activate edge in the nervous system. What are other things we can think about, What we're interested in as well is that these kappa opioid receptors. So we all are very familiar with mu opioids such as morphine or uh and the various uh fentaNYL and all these pain mitigating drugs which are also highly addictive. But the mu opioids we know where generally associated which can with which can induce itch can activate it. But we also know that there are endogenous pathways uh mule non mu but actually kappa opioid pathways which counterbalance mu so if you activate mu opioids you get rich if you activate capital opioids suppress it and it's this counterbalancing that results in homeostasis. Um Well in fact we know that there are drugs for instance like such as naltrexone that blocks the opiate receptor and it could be somewhat effective in it. We know that they're kappa opioid receptor agonists such as more recently developed Heflin but then there are also dual mechanism uh agents that actually block the mu opioid receptor and agonize the kappa opioid receptor and optimize perhaps perhaps to mitigate edge. And these drugs include but are final and the more recently developed beauty if you actually look again at the single cell RNA sequencing data sets. If you look at the kappa opioid receptor, what we find interestingly is that in fact the mu opioid receptor is very much enriched within these ich C fibers here shown in yellow. We don't detect the kappa opioid receptor within these itch neurons. Rather we find that these kappa opioid receptors are on the touch neurons shown here. So what we think is in fact mu opioid probably activate it within the periphery by activating these itch neurons. Excuse me here. But what we think actually is that the kappa opioid serve at least in the periphery to suppress it by activating touch receptors and touch neurons that then in the spinal cord actually suppress it and block these nerve fibers. The kappa opioid agonist course uva or develop Coughlin has actually been approved in the United States in the last year for the treatment of your E. Mc peratis associated with hemodialysis. So we believe that this is actually a very viable therapeutic pathway In the laboratory. We've actually used the decathlon in our mouse model of a topic dermatitis. We found no effect on the disease whatsoever. As you can see here no effect on the inflammation. But what we found is very rapid effect in terms of the itch shown here, independent of the inflammation very rapid. Within 30 minutes we see an effect on the itch and interestingly what we find is that the default calphalon in and phase two clinical trials in a topic dermatitis is really generally, what we find is it's effective and mild to moderate a topic dermatitis. In in other words, if you have a low inflammatory burden but persistent itch, these patients respond in hyper inflammatory or very significant large body surface area involvement. It is hard to treat it and a topic dermatitis because this drug is largely neuromodulation. Ori in other words, treating an inflammatory itch with neuromodulation is a harder task. You do want to get rid of the inflammation. But what we think is that this kind of mechanism actually may be better suited for neuromodulation in the context Of neuropathic itch conditions. So what kind of condition are we talking about? Natalja, para aesthetic and nostalgia, para aesthetic. A is it on the back? It's why the back scratcher was likely invented. It's many people suffer from it, some suffer from it very severely. This is not an inflammatory condition. This is a truly neuropathic neurogenesis condition. And this drug has actually been shown to be very effective in Phase two clinical trials which just read out this summer. So what we think is that there, as I mentioned already, there are sad akin's and Luca trains and other factors that may actually stimulate each specific neurons that result in the perception of it. But then that there are drugs such as delightfully Kathleen or even now Bluefin which may actually serve to suppress it by acting other sensory neurons that may be much more mechanical receptive. Um you know, we wrote a perspective recently saying that, you know, the investment in its research in the United States has actually been very, very low. It's just not been taken very seriously. It was not really considered a serious medical problem until very recently. But as you show, as we show in the table on the right the success of targeting its pathways and I'm just showing even subsequent to writing this article, for instance, the data and nostalgia yet another successful clinical trial. This is the the success rate has been incredibly, incredibly good. So, the return on investment in this area of science and medicine has been quite fantastic. But what we are also finding is that even within the body cavity, for instance, the vagus nerve is sensory, but not only is it sensory, what we find is that in fact there are subsets of Vegas neurons that are actually in fact which resemble resembling the itch neurons that I've been talking about throughout this talk, Mp one mp two mp three here. So why do does the vagus nerve that innovates the body cavity and the visceral organs actually have? It's like properties we actually think essentially what is happening is that the vagus nerve is very much sensory. So, if you look at the Samantha sensory nursing the dorsal root ganglia, they are very much Trip V one positive. You look at Trip V one reporter mice, but if you look at the vagal ganglia, you see these Trip V one positive neurons, you are essentially indistinguishable. And we think of trippy one as being a marker for sensory neurons in many ways. So what we think is that in fact uh the itch is actually a model for kind of other kinds of noxious sensations, perhaps even from within the body cavity. And in fact, what we find is that much like kappa opioid agon is um for for for rich as a strategy for itch Trevi therapeutics which has developed now abusing which is a kappa opioid agonist receptor agonist. Uh what they found is that it has actually efficacious and phase two clinical trials in cough as well. And we think of cough as being a kind of sister to itch. Uh and Essentially, the way we break this down is what we've been studying is it and these itch neurons are somatic reference, but we also know that the vagus nerve is approximately 80% sensory as I've been hinting at already. My apologies and in many ways, by studying it, we can actually start to understand perhaps noxious sensation from visceral organs, such as the lung, the gut and other organs as well. Also the spinal visceral Africans that also come from the DRG we know very little about and we feel is a major new frontier. So the idea is not just itch, but how do we sense things from the outside, through the skin, but also from the inside and intercepted fashion. And we feel that it represents a great sense of paradigm to actually probe this kind of biology. We also know in recent studies that itch uh specific or itch identity neurons exist even within the trigeminal ganglia in mice in humans. One of the interesting things as you go from mouse to humans that these itch like neurons within the trigeminal ganglia in the context, they've been migraine headaches studied in the context of migraine headaches have much more expression of Cd R. P alpha. In other words, these neurons in humans not only have each like properties but also have properties that indicate our highly suggested that they can release in europe appetites, particularly GRP alpha neuro peptide that is already a therapeutic in the context of migraine headaches. So we I think that it actually represents a paradigm of irritation in many ways. Perhaps we know that there's itch, but this may help us to understand cough headache, reflux, nausea, irritable bowel interstitial cystitis and many other conditions. And so we started by trying to understand what causes chronic itch and we've been able to reverse translate this into mice to understand fundamental new immunology that's informed the development of new therapeutics clinical trials and from clinical trials we've been actually able to reverse translate against identify new forms of acute itch and perhaps revise sensory paradigms. I'd like to end by thanking all the members of the laboratory to put the work in. I bolted the individuals who led the work that I showed here in particular from all around the world. I I wanted to highlight zen wang here who invited me uh here with Professor Wong for this talk, who is now in my laboratory and has a fantastic, wonderful project which hopefully in the near future we will represent is a superstar. I'd like to thank all the funding agencies that supported our work, our wonderful collaborators as well. So thank you very much for having me and it's a great honor to be able to present our work here today. Thank you. Professor Kim give us a very wonderful lecture. I think you did a lot of basic and clinical try on the each and uh achieved a lot. Congratulations. Because time is limited and also just you know on the line. So maybe in the future welcome to changing giving a lecture and that we can discussion deeply. Thank you. Yes, I would love to come to china. I have actually not been to china yet. So hopefully someday. Okay, thank you. Thank you