Because of natural exposure to wildfire smoke, nonhuman primates have provided an increased understanding of the long-term effects of smoke inhalation during infancy, shares Lisa Miller, University of California Davis (UC Davis). Dr. Miller also discusses with co-hosts Anne Chappelle and David Faulkner the importance of animal models in human health research and how nonhuman primates can be good models for vaccine testing, as was the case with COVID-19.
About the Guest
Lisa A. Miller, PhD, is a Professor for the UC Davis School of Veterinary Medicine and serves as the Respiratory Diseases Unit Leader for the California National Primate Research Center. She also is the principal investigator or co-investigator for 15 active research grants.
Dr. Miller’s research focuses on investigating the impact of environmental exposures (air pollution, allergens, microbes) on pulmonary and immune system development during the first year of life. She uses both cell culture approaches and animal models to address questions related to mucosal immune mechanisms in pediatric populations, with an emphasis on understanding the etiology of childhood asthma and susceptibility to infectious disease.
Dr. Miller earned her BS and PhD from UC Davis and was a postdoctoral fellow in the Stanford University School of Medicine.
[00:00:00] Adverse Reactions “Decompose” Theme Music
[00:00:05] David Faulkner: Hello, and welcome to Adverse Reactions, Season 2. My name is David Faulkner, and this is my co-host,
[00:00:11] Anne Chappelle: Anne Chappelle.
[00:00:12] David Faulkner: As much fun as the first season of Adverse Reactions was, I think Season 2 is better.
[00:00:16] Anne Chappelle: Hidden.
[00:00:17] David Faulkner: Secretive.
[00:00:18] Anne Chappelle: Exactly.
[00:00:19] David Faulkner: The toxicology that happens when you’re not looking,
[00:00:22] Anne Chappelle: or toxicology that you forgot about.
[00:00:24] David Faulkner: It’s still important, and we’re here to talk about it. Welcome to Season 2 of Adverse Reactions:
[00:00:28] Anne Chappelle: “Hidden Toxicology.”
[00:00:31] Adverse Reactions “Decompose” Theme Music
[00:00:38] Anne Chappelle: Of Monkeys and Men.
[00:00:40] Lisa Miller: Rhesus macaques, which is what we have here at our center, can get COVID, and they are a critical animal model for the testing of vaccines. In fact, all of the vaccines that we are using currently have been tested in rhesus macaque monkeys that have been experimentally infected with COVID-19, or SARS-CoV-2, I should say.
[00:01:00] Anne Chappelle: Or, Lisa Miller Says, “Wildfire Smoke Isn’t Monkey Business.”
[00:01:05] Lisa Miller: Based upon the imaging studies, it would suggest that the animals have some functional deficits in their respiratory tract, so we’re going to test that by putting activity collars around them. So, basically, a variation of the Apple Watch is going to be in the collars.
[00:01:23] Adverse Reactions “Decompose” Theme Music
[00:01:27] Anne Chappelle: Welcome, Lisa, to our show. I’d like for you to introduce yourself, please, to our listening audience.
[00:01:34] Lisa Miller: My official title is Professor at the School of Veterinary Medicine at the University of California Davis. The other hat that I wear is I serve as the Associate Director of Research here at the California National Primate Research Institute, and I also lead the respiratory diseases research group out here at the primate center.
[00:01:56] David Faulkner: Well, you say primate research, and I’m thinking, is it apes with pipetters and lab coats? It’s a great visual; I’m really enjoying that.
[00:02:05] Lisa Miller: No.
[00:02:07] David Faulkner: Darn.
[00:02:08] Lisa Miller: We have our investigators out here doing that.
[00:02:11] David Faulkner: Oh, OK.
[00:02:11] Lisa Miller: So, the California National Primate Research Center is, oh, gosh, I believe we’re one of seven—because it’s shifted over years—National Primate Research Centers. There are other small primate centers across the country, but there are basically seven large NIH-funded centers. So, what does that mean? These are centers that are dedicated to nonhuman primate research, so the programs vary across the country. So, the California center is located off-site of the UC Davis campus. As you would imagine, housing, caring for, raising nonhuman primates not an inexpensive process, so we really rely on the support of the National Institutes of Health to provide the basic infrastructure for our centers. In terms of the overall acreage, we have, I think we sit on about 300 acres out here. Depending upon what season of the year, upwards of 5,000 nonhuman primates.
[00:03:15] Anne Chappelle: Wow.
[00:03:16] Lisa Miller: Yeah, that’s always a surprise to folks.
[00:03:18] Anne Chappelle: That is a barrel of monkeys.
[00:03:20] Lisa Miller: It is truly a barrel of monkeys, yes. These are rhesus macaque monkeys. Some of these animals are quite large and about half of them live outdoors in what we call field cages that are about half acre in size, so it’s about half of a football field. They live in family units outside, and they breed in family units outside. So, it’s a terrific opportunity for those us who are studying effects of environment and studying the effects of environment on various aspects of nonhuman primate health. We also have, not surprisingly, a lot of investigators out here are behavioralists. And we are a consortium; we communicate frequently in terms of the research that we do and the programs that we offer. We’re all very tightly connected on a national level, which allows you to also look very broadly across the country in terms of what’s happening research-wise in the various centers. So, that’s a fun part of the job.
[00:04:20] Anne Chappelle: When I think of nonhuman primate research, I tend to think of some of the contract labs with their research in pharmaceuticals or whatever. So, this isn’t anything to do with those kinds of research projects. Is that true?
[00:04:35] Lisa Miller: The centers do support some industry contracts if in fact we have room and the capabilities to support those sorts of studies, but we try to focus on those studies that really are intellectually rewarding us. For example, I’m a respiratory biologist and had an opportunity several times over the past years to test new compounds that are going into preclinical trial for asthma. When those sorts of opportunities come up, and I think of them as opportunities because you really want to able to take the animal models that you’ve developed and see that research translate into the clinic. That’s why we work on nonhuman primates. In that sense, we can do some industry contracts, but the bulk of it, I would say, is focused on NIH-supported as well as some NSF-supported research. So, lots of infectious disease. As you would imagine, COVID has been a major focus in the past year and a half for all of us.
[00:05:39] Anne Chappelle: They get COVID? The nonhuman primates?
[00:05:41] Lisa Miller: Yes.
[00:05:41] Anne Chappelle: Wow.
[00:05:42] Lisa Miller: Not all species, but rhesus macaques, which is what we have here at our center, can get COVID, and they are a critical animal model for the testing of vaccines. In fact, all of the vaccines that we are using currently have been tested in rhesus macaque monkeys that have been experimentally infected with COVID-19, or SARS-CoV-2, I should say.
[00:06:04] Anne Chappelle: Wow. I did not know that.
[00:06:07] Lisa Miller: It’s been an interesting year in the past year and a half because of all of the issues with the pandemic, we have to provide animal care 24-7 for a large group animals that are susceptible to SARS-CoV-2. So, we had to keep our animals uninfected and healthy as well as keep the humans caring for those animals uninfected and healthy. So, that was quite a challenge.
[00:06:31] David Faulkner: This is a heroic thing. Especially, I’m thinking, March of 2020, we had no idea what the situation would be, how the virus was transmitted most readily. So, what was that like, trying to adapt, knowing that there’s this big mystery event, but you’ve still got to do your job and take care of these animals?
[00:06:52] Lisa Miller: It was extremely stressful. Fortunately, because of the issue of disease transmission, actually both ways—between humans to the monkeys as well as monkeys to humans—we already have safety procedures in place. So, if you are directly handling an animal, you have tremendous amount of PPE. That protocol is already in place. So, it was actually simply a matter ratcheting it up so that all of us coming in and out of the facility had to wear masks, which is what we’re all used to now, and we’re continuing to do that. That, I believe, has been really the key mitigating factor in keeping our animals healthy. Actually, all of the centers have been very fortunate in that all of our animals were able stay healthy.
[00:07:41] David Faulkner: People have different ideas about the roles of animals in research. I’m curious: How do you talk about the role of animal models, especially because nonhuman primates, there’s something more visceral there, I think, rather than just mice?
[00:07:55] Lisa Miller: It’s a sensitive subject for lot of people, and I certainly am aware of that. I respect everybody’s opinions in terms of animal research. What I try to emphasize is the importance of this animal model. This is really the step between the early-stage studies in rodents and taking a drug, for example, to the clinic in humans. I try to emphasize that monkeys play a critical role in taking a basic observation in the laboratory to a human clinical trial. For the purposes of safety, for the public, it’s important to do those initial tests in a relevant animal species before going into a human being, and it’s particularly important for some of the work that I do with nonhuman primates where our interest is very focused on the first year of life, so infants, babies, that’s a very sensitive window for a lot of environmental exposures. We have a lot of observational data in humans in the sense that we can track children in terms of if they develop health outcomes if they live in areas that are heavily polluted. So, we can do those sorts of observational studies, but in terms of providing definitive mechanistic proof, we need to have those relevant animal models to confirm, scientifically, in an experiment, that Pollutant A causes asthma in a child if they’re exposed to high levels of it. Our regulatory agencies absolutely need that information. From the perspective of toxicology, you need to use multiple animal models, and in fact, my laboratory does use rodents for some of our initial, early-stage observations and experimental testing. And then we go to the nonhuman primate as our proof of principle studies. But in many cases, particularly for studies that involve studying the immune system, for example, the immune system of nonhuman primates and humans is very unique in terms of the timing relative to birth; that’s a process that is very difficult to recapitulate in mouse studies.
[00:10:27] Anne Chappelle: I also am interested in the upper respiratory tract, and it is very difficult to do these things in mice and rodents because they are obligate nose breathers, so you get a lot of scrubbing and that’s different. It’s really hard to get enough tissue sample, and just seeing some of the differences from a handling standpoint, I can see why you really would rather have a larger set of lungs that is more relevant to what I would deal with. I understand the push for alternatives, but—
[00:10:56] Lisa Miller: I think of this, you know, I’m a parent and even though my daughter is an adult now, you want to make sure that all of the critical testing that is needed to ensure a drug, a vaccine, whatever, that is going into your child has been tested to the best of our ability. No matter how sophisticated a computer design algorithm for drug testing is, you can’t recapitulate the immune system, the respiratory system, of a child. I think it’s important to emphasize also that in terms of overall numbers of animals, if you really look at the numbers, the numbers of nonhuman primates that are used in studies relative to rodents is really miniscule. We consider the nonhuman primate as the proof of principle study, and it’s only done after numerous studies have taken place in a large number of smaller animal species.
[00:11:53] David Faulkner: What drew you to do this work in the first place, to work with primates, and also what sort of students are attracted to this work?
[00:12:01] Lisa Miller: I can tell you, I literally stumbled into it, and I think that happens all the time, right?
[00:12:08] Anne Chappelle: The best research you stumble into.
[00:12:11] David Faulkner: Trip over a monkey when you’re walking through the hall.
[00:12:13] Lisa Miller: That’s right. When I started off, I was a postdoc and I actually had moved from my postdoc position at Stanford back to UC Davis. I jumped into the respiratory group because I had worked previously with a faculty member in the respiratory group out here. And this group was given a challenge specifically by NIEHS because this group at UC Davis, primarily led by Charlie Plopper, had really contributed a significant amount of important data on ozone and ozone-related toxicology and modeling some of the health impacts of ozone in small numbers of nonhuman primates. So, NIEHS came back to Charlie and said, “We think this is important, but we really want to understand how air pollution affects the development of asthma.”
I had literally just started as a postdoc at that time. None of us knew how to do an asthma model. I had a lot of training in immunology before coming back to UC Davis, and I thought, wow, what an opportunity to come in literally on the ground floor, develop a model. And I thought, geez, this an incredible opportunity to take what I’ve learned both in the respiratory tract as well as in immunology and move it forward. So, that’s how I started, was in the development of a nonhuman primate asthma model. And in fact, we were the only group nationally, internationally, that had this animal model in monkeys using house dust mite, and we showed, through a series of the publications, that air pollution exposure concurrently can really exacerbate the development of asthma, particularly in young animals. So, we were modeling development of childhood asthma and how air pollution exacerbates that. So, that’s how I got started.
So, the students that I currently have, they’re all immunology students. Actually, I take that back; I have one pharmacology student. But they’re attracted to the same sort of vision of wanting to work with a species that is highly translatable to humans. The building that I’m in is maybe 50 feet away from our field cages, so you see that the animals are getting exposed to wildfire smoke, for example, and you can translate that back into the laboratory. So, that’s what attracts them. A lot of my students actually end up going into industry, which I fully support. I want them to do what they’re happy and interested in doing.
[00:14:47] Anne Chappelle: Do call yourself a toxicologist?
[00:14:50] Lisa Miller: Would I call a toxicologist? On a good day.
[00:14:55] Anne Chappelle: You’ve got so much of this veterinary DVM background. Your students, you said a lot of them have the background in immunology. Are they coming out with an immunology degree? Are they coming out with a tox degree or pharmacology degree? How do your students leave you?
[00:15:11] Lisa Miller: I would call them immunotoxicology. So, I can call myself a toxicologist in that actually it’s a course that I’m teaching right now, this quarter, for our toxicology students is trying to understand how toxicology, toxicants, influence the immune system, because that’s primarily how air pollution, we believe, in part influences the development of diseases such as asthma.
[00:15:37] David Faulkner: There’s a lot of incredible work that comes out of UC Davis’s tox program, especially this work on wildfire smoke that you’ve alluded to. I feel like we’ve been saving this delicious dessert, or rather, it’s like you’ve got several on your plate, you eat few things, and it’s like, alright, time for the potatoes. Let’s dive in. So, let’s dive into the potatoes, the wildfire smoke research that you’ve done. Can you give us the top line of it, and then we’ll dig in from there?
[00:16:00] Anne Chappelle: Give us the 35,000 smoke level.
[00:16:04] Lisa Miller: The focus of the work that we’re currently doing is to study the immune system response to pathogen mimics as well as respiratory remodeling in a cohort of animals that were exposed to high amount of wildfire smoke back in 2008.
[00:16:25] David Faulkner: Wow.
[00:16:25] Lisa Miller: As far as I’m aware, we’re the only group that actually has data on long-term health outcomes, albeit in a monkey, but we’re able to track that health outcome and able show that, in fact, there are pretty striking differences in terms of animals that were exposed outdoors to that wildfire smoke.
[00:16:46] David Faulkner: So, what specifically do you see? What happens to these young monkeys that were exposed to wildfire smoke?
[00:16:53] Lisa Miller: So, two things in our observation, and I should make clear that the beauty of what we’ve been doing in terms of tracking health outcomes in our colony is that we’re able to do everything noninvasively. We’ve not tracked the same animals over time, but we started with a fairly large cohort. We have maybe four or five hundred animals that are born each year in our colony because we are a breeding colony. So, we have four or five hundred baby monkeys running around outside in our field cages during the summer. That’s what happened during this particular event, and so we’re able to sample periodically as the animals mature. Now, some of them go off and go on to studies, but there’ve been a fair number left. And so, now, they’re 13 years of age, which makes them mature adults.
So, what we’re able to do is for the respiratory tract, we’ve actually been able to image the thoracic cavity. And we use CT scans to do the scans, and then also we work with a company that has basically an AI approach to quantifying structural changes so they can show airways remodeling through the imaging. So, we’ve been able to track that and it’s very clear, crystal clear, that the monkeys that were exposed to this wildfire smoke when they were babies, when they were infants running around in the field cages, have now what appears to be some type of an early-stage fibrosis or interstitial lung disease.
[00:18:28] Anne Chappelle: Wow.
[00:18:28] Lisa Miller: Yeah, it’s pretty stunning. So, that’s the lung. And then, when we take a blood sample from the animals and we bring it into the lab and then we culture the blood with toll-like receptor ligands, which if you’re an immunologist, that triggers innate pro-inflammatory response. The animals that were exposed to wildfire when they were youngsters, right now, they have this hyper-inflammatory response. Initially, they have a suppressed immune response, and then, it’s now reverted into a hyper-response.
[00:19:02] Anne Chappelle: So, I kind of call that, like, a twitchy lung.
[00:19:04] Lisa Miller: Yeah, could be. We’ve not challenged animals with like an allergen or anything of that nature; we’re mostly focused on structural changes at this point in time. One of the cool things that we’re going to do is, based upon the imaging studies, it would suggest that the animals have some functional deficits in their respiratory tract, so we’re going to test that by putting activity collars around them. So, basically, a variation of the Apple Watch is going to be in the collars.
[00:19:36] David Faulkner: Nice, nice.
[00:19:37] Lisa Miller: So, what we’re going to do is actually quantify their activity levels to see whether they in fact do have changes in their activity relative to their unexposed counterparts.
[00:19:47] David Faulkner: Fascinating.
[00:19:49] Anne Chappelle: I was just imagining, they’ve got all of this, texting each other with their Apple Watch.
[00:19:54] David Faulkner: But there’s a lot of trust involved because they can’t see the screen.
[00:19:57] Anne Chappelle: That’s true.
[00:19:58] David Faulkner: “Hey, Bill. Can you respond? What is Marcy saying?” So, if I understand this right, the idea is that if you have child that is exposed, or an infant, exposed to wildfire smoke, it’s possible, and what you’ve seen, it suggests that it affects the lungs for the rest of their lives.
[00:20:13] Lisa Miller: Precisely.
[00:20:14] David Faulkner: And the immune system.
[00:20:15] Lisa Miller: Yes.
[00:20:16] Anne Chappelle: What were the levels of the smoke? Because I don’t remember. Were these animals exposed for a week, a month?
[00:20:22] Lisa Miller: So, we have Air Resources Board Air Quality Monitor just down the road, fortuitously, so we have the PM2.5 data available to us. It was one week acute exposure, and then it went away, wind conditions changing, and then it came back for another week. So, it’s basically just two weeks’ worth of exposures, but the exposures were at the highest level: two to three times above our air quality standards. I get asked, What made you think of doing this? And can tell you, I was sitting in my office, and I’m looking out the window, it’s June and it looks like the middle of winter because it looks like fog—that’s how intense the smoke was. So, it was clearly visible. That’s what the animals were being exposed to.
[00:21:10] Anne Chappelle: Wow.
[00:21:11] David Faulkner: Monkeys in the mist.
[00:21:12] Lisa Miller: Monkeys in the mist. Yeah, exactly.
[00:21:15] David Faulkner: So, you’re looking at PM2.5. These are characteristic smoke particles. So, we’re thinking about, say, living next to a highway or in a city with a lot of auto traffic or other countries where there’s lower emissions standards. You see all this with wildfire smoke. Does this also apply to other types of smoke? Or at least, should we think in that direction? Maybe it’s not a one-to-one.
[00:21:38] Lisa Miller: That is the conundrum that the field has now with all of the investigators now trying to study wildfire smoke. It’s a very complex mixture; it’s highly variable depending upon what is being combusted, what species of biomass, and then, throw in all of the man-made products that could potentially combust along with it, then how old the smoke is, and I mean, there’s so many factors involved. So, that’s one thing. And then, we know now that—well, I guess this is a little bit controversial—but in my opinion, if you look at data very carefully in terms of PM2.5 exposures globally, it’s very clear that not all PM2.5 is the same chemically. And especially if your readout is health outcomes. So, not all PM2.5, for example, elicits asthma; sometimes, you get other types of respiratory conditions like interstitial lung disease or COPD. I think that those are important clues to us as scientists that not all PM2.5 is the same in terms of chemical makeup. And I think that’s been demonstrated. And I think that would translate into health outcomes in people that are being exposed to it. We just need to figure out what is that magical chemical composition that translates into fibrosis versus COPD versus asthma. I don’t think we’re there yet.
[00:23:08] David Faulkner: It does seem like kind of an academic question: lung disease is lung disease. And I guess if we can say, like, exposure to smoke is bad, perhaps that’s enough start taking action.
[00:23:18] Lisa Miller: We clearly need more research in understanding what those mixtures are. I mean, that’s something that we’re planning in the lab now. We’ve got the observational data outdoors; the next step is to confirm it experimentally. What we’re planning to do is use wood smoke particles in combination with other components like phthalates or other chemical constituents that have been picked up on in some of these mixtures, add those back to see what are the key triggers, and I would start with a cell culture dish and move into the animal models.
[00:23:55] David Faulkner: To clarify, when I say it’s an academic question, I don’t mean to be dismissive.
[00:23:59] Lisa Miller: No, it’s important. It’s important.
[00:24:00] Anne Chappelle: So, when I was doing my background research, it seems like you have a ton of active grants. You’ve got a huge teaching load. You’re doing this great work. You’re mentoring others. You’re talking to us. When do you have time to do all of this? How do you focus on any one thing, to be honest, because you’ve got your irons in lots of fires. It’s very impressive.
[00:24:26] Lisa Miller: Well, thank you. That’s very kind of you. I think that’s the expectation of faculty, right? We’re supposed do it all and juggle a million things. That’s just what we’re supposed to do.
[00:24:36] Anne Chappelle: That’s got to be hard, too, on a personal life.
[00:24:38] Lisa Miller: I would say, to be honest, I believe in self-care. I exercise regularly, religiously, and that’s probably, that’s my self-care—it’s not everybody’s self-care—but I think it is important carve out that time. If you take care of yourself, you can take care of others and do the balancing act and stuff.
[00:24:57] David Faulkner: It’s a good message.
[00:24:58] Anne Chappelle: So, we also have a number of questions that we ask.
[00:25:01] David Faulkner: What is the most significant adverse reaction you’ve experienced in your life?
[00:25:07] Lisa Miller: I have deathly response to mussels. Never feed me mussels. No paella for me.
[00:25:15] David Faulkner: A pity. What would you be doing if you weren’t doing you were doing right now?
[00:25:19] Lisa Miller: Maybe I would be a spin instructor or something.
[00:25:22] Anne Chappelle: I could see you motivating everybody at SoulCycle.
[00:25:25] David Faulkner: That’s a good one. Low impact. Very important.
[00:25:28] Lisa Miller: Low impact. That’s right.
[00:25:29] Anne Chappelle: I’ve learned a ton today.
[00:25:31] David Faulkner: Yeah, thank you so much for joining us. This has been a lot of fun. We’re so glad to have you.
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[00:25:42] David Faulkner: That’s Season 2.
[00:25:43] Anne Chappelle: I’m done talking.
[00:25:44] David Faulkner: Done.
[00:25:44] Anne Chappelle: Love it.
[00:25:45] David Faulkner: Alright, I’m going to stop the recording because I think we’ve got it.
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[00:25:51] Anne Chappelle: Thank you, all, for joining us for this episode of Adverse Reactions, presented by the Society of Toxicology.
[00:25:57] David Faulkner: And thank you to Dave Leve at Ma3stro Studios.
[00:26:00] Anne Chappelle: That’s Ma3stro with a three, not an E.
[00:26:03] David Faulkner: Who created and produced all the music for Adverse Reactions, including the theme song, “Decompose.”
[00:26:09] Anne Chappelle: The viewpoints and information presented in Adverse Reactions represent those of the participating individuals. Although the Society of Toxicology holds the copyright to this production, it has,
[00:26:20] David Faulkner: definitely,
[00:26:21] Anne Chappelle: not vetted or reviewed the information presented herein,
[00:26:25] David Faulkner: nor does presenting and distributing this podcast represent any proposal or endorsement of any position by the Society.
[00:26:31] Anne Chappelle: You can find out more information about the show at AdverseReactionsPodcast.com,
[00:26:37] David Faulkner: and more information about the Society of Toxicology on Facebook, Instagram, LinkedIn, and Twitter.
[00:26:43] Anne Chappelle: I’m Anne Chappelle.
[00:26:44] David Faulkner: And I’m David Faulkner.
[00:26:45] Anne Chappelle: This podcast was approved by Anne’s mom.
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[00:26:53] End of Episode