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[00:00:37] Dr. Briana de Miranda: Thank you for having me. It's a pleasure to be here.
[00:00:40] Prof. Tiago Outeiro: Briana, I wanted to start from the beginning, and I wanted to ask you when you started working on the connection between pesticides and Parkinson's disease, and what made you work on this topic at the time when you started?
[00:00:53] Dr. Briana de Miranda: Yeah. So I've actually worked on this topic for most of my academic career. I started this [00:01:00] when I began my graduate training in toxicology and many toxicologists focus on the way that chemicals interact with the brain. And one of the main ways that this is studied in the toxicology field is the impact of environmental exposures on Parkinson's risk and the mechanisms behind how these toxic chemicals can actually either kill or impair dopaminergic neurons and thus leading to Parkinson's risk.
[00:01:28] Prof. Tiago Outeiro: So you already started to mention dopaminergic neurons. So what do we know about how pesticides may increase the risk for Parkinson's?
[00:01:39] Dr. Briana de Miranda: One of the sort of central mechanisms that is, is pretty common to most pesticide exposures or pesticide types is this idea. That they create some kind of pathology within dopaminergic neurons that leads to the selective vulnerability of their either cell death or or [00:02:00] degeneration or pathology.
And there's a lot of different ways that this can happen based on a chemical to chemical basis. But 1 of the sort of central tenants is this idea of either oxidative stress or mitochondrial dysfunction. Both of which we think are really important in dopaminergic neurons because of their sort of intrinsic vulnerability to those types of pathology.
[00:02:24] Prof. Tiago Outeiro: And in this topic of mitochondrial dysfunction, usually we hear about inhibition of mitochondrial complex one. Do all pesticides work in the same way by affecting mitochondrial complex one? I mean, you mentioned already oxidative stress, but Do we know how different pesticides may work and why they may all, in the end, apparently affect dopaminergic neurons?
[00:02:51] Dr. Briana de Miranda: So that's a really great question. We know how some pesticides work and some of them are really kind of classic toxicants [00:03:00] in that way. So if you take, for example, the pesticide rotenone, this is an organic pesticide. It's found in nature and when you synthesize it and apply it In high concentrations, it's a really great pesticide and it's also a classic complex 1 inhibitor in the mitochondria.
So that's really 1 of the very 1st chemicals that we discovered to have a specific mitochondrial target and that led directly to the selective degeneration of dopaminergic neurons. Especially in animal models, which is, which is where rotenone is often used. There are other pesticides, if you take, for example, the pesticide paraquat, which is a broad spectrum herbicide.
That is not clear that that's a direct mitochondrial complex 1 inhibitor. Instead, it's very likely acting. At numerous places in the cell to induce a lot of oxidative stress. So, for example, it may cause redox cycling in the cytoplasm, which could then in turn damage the [00:04:00] mitochondria as well as other cellular macromolecules and it could also have direct action at the mitochondria as well.
So not necessarily everything has to affect complex 1 at the mitochondria to induce similar types of damage within dopaminergic neurons and surrounding cells in the brain.
[00:04:18] Prof. Tiago Outeiro: And when we think about Parkinson's, we know that genetics explains only a fraction of cases. Environment of course is important, but we know that we need to understand this relationship between genetics and environment. So are there known genetic factors that can make people more susceptible to pesticides?
[00:04:37] Dr. Briana de Miranda: Yes, there have been really great epidemiological studies again, that have pointed us towards what. genetic susceptibility factors might increase your risk for either many pesticide exposures or specific ones. So, for example, one of the most common metabolizing enzymes, the cytochrome P450 family the isoenzyme CYP2D6.[00:05:00]
If you have a polymorphism in this particular enzyme, you may be at more risk for maybe maybe Parkinson's risk if you have pesticide exposure. Another one is PON1 gene called PON1 and organophosphates have been associated with elevated risk. And then there's others that are not associated with metabolizing, but with how much chemicals can get into the brain.
So, if you think about transporter polymorphisms, like the ABCB1 variants, and that may lead to differential amounts of, of chemicals being able to get into the brain as well as maybe different polymorphisms in the HLA-DRA genes. So, so in your inflammatory genes and pesticide exposure.
So that's kind of a, I listed off many there, but you can kind of think of this as risk factors in metabolizing enzymes, transporters to transport chemicals across the brain, as well as other more broad risk factors [00:06:00] like inflammation.
[00:06:01] Prof. Tiago Outeiro: And and so to study all of these, these modes of action of these different substances how have you and, and of course other colleagues studied the effects of these, these substances in the brain? Can you briefly tell us about existing models that you're using? Because you and I, we are basic scientists, so we, we don't normally work with patients, but how do we study these things in the lab?
[00:06:26] Dr. Briana de Miranda: Yes, that's right. We, we have to translate this into the lab to study this experimentally and understand the mechanisms. One of the ways that I did this with, especially during the time that I was At the University of Pittsburgh, working with Tim Greenamyre is using the pesticide rotenone and what's really fascinating about the quote, rotenone model of Parkinson's is that you inject rotenone systemically into animals and it results in the selective loss of dopaminergic neurons.
And so it really shows that vulnerability of dopamine [00:07:00] neurons to this systemic chemical. And so we can do this in rats. We know we, we basically treat them for a couple of weeks with rotenone, and they degenerate over time, progressively, much like an accelerated version of how people might progress with Parkinson's disease.
And so, at the end of the experimental study, we take their brain tissue, and we assess many different things, but. You know, the, the most important is looking at, how this pathology and dopaminergic neurons is driving what we would consider traditional pathological hallmarks of Parkinson's, including things like accumulated alpha synuclein and neuroinflammation.
And of course, the loss of dopaminergic neuron.
[00:07:40] Prof. Tiago Outeiro: And, and one thing that of course we are all intrigued with is this apparent dopaminergic sensitivity. And we know there's many different types of neurons in the brain. They all perform slightly different functions. They, they communicate using different neurotransmitters. So why [00:08:00] do we think that these dopaminergic are more sensitive than, than others?
[00:08:05] Dr. Briana de Miranda: Yeah, that's a very difficult question to answer because the sort of most obvious answer is we don't really know there is a lot of hypotheses. One is that they require a lot of energy in order to maintain sort of their their day jobs. Right? So producing dopamine as well as they have really heavily branched axons that require a lot of energy to maintain.
So, both of those things are really important for mitochondrial function and anything that would disrupt that could lead to dysfunction within the neuron. They're really highly sensitive to oxidative stress. Part of this could be because they produce dopamine and dopamine itself may be considered an oxidative molecule.
So they may start off with a lower antioxidant capacity because, you know, as their sort of regular day to day activity includes needing [00:09:00] antioxidants in order to take care of any oxidative sort of dopamine leftover in the cell. And so they require a lot of, of things in order to stay healthy.
And so any disruption in that can ultimately lead to their, to their death. And while other neuron populations. Are certainly, potentially vulnerable in other ways. We really don't see the selective loss of other cell populations to environmental chemicals the way we see in dopaminergic neurons.
And so I think there is still somewhat of a mystery that remains in why these cells are so exquisitely sensitive to specific environmental toxicants. And that's, of course, one of the things that my lab is continuing to study.
[00:09:44] Prof. Tiago Outeiro: And since we know pesticides are important for agriculture and it doesn't seem to be so easy to replace them with molecules that, that will do the same job without having some of these undesirable side effects. So [00:10:00] are there any known molecules that, that are known to counteract perhaps the effects of pesticides that one can look at?
From a therapeutic perspective, perhaps.
[00:10:11] Dr. Briana de Miranda: Yeah, also a really important topic in the neuro toxicology field is to assess how we can protect these cells. I think one of the most obvious ideas that has come out is that we could maybe treat with an antioxidant in order to counteract these oxidative stress actions that are happening with with toxicant exposure and this works quite well experimentally.
So we can. See, you know, if we treat an animal with an antioxidant and then we treat them with rotenone, they might be protected against degeneration. We can do this with Paraquat and other different toxicants as well. But what's really interesting is that when you take that and you translate it into human Parkinson's disease, these antioxidants, That have been shown experimentally to be protective against [00:11:00] these specific toxicants have not really been protective and Parkinson's.
And so I think there's a lot of question about whether, you need to intervene right at the point of exposure, which, of course, most of us don't know when we're being exposed to these things. So, you know, if there was a way. That we could use a strong antioxidant or something that that's been proven experimentally to protect against the toxic effects of these, these compounds at the time of exposure.
That might be a potential therapeutic strategy. But certainly experimentally, we can block this in a number of different ways.
[00:11:34] Prof. Tiago Outeiro: No, that's so there's there's hope. So that's that's good. And in terms of open basic questions that we still have to address that, for example, you are addressing in your lab, what do you think are the most important unresolved issues that we should really try to address? In the coming years. So we understand how pesticides are working and what we can do to avoid, of [00:12:00] course, we can stop using them.
And this is an important thing to do for some of these. But is there anything else that basic science is telling us that we need to do in order to address this very important topic?
[00:12:13] Dr. Briana de Miranda: Yeah, absolutely. So, one of the things that my lab is really interested in, and it's sort of tangentially related to this is the idea that it's not just pesticides that increase risk for Parkinson's. And so we've been studying really heavily this organic solvent called trichloroethylene. That's going to be a different kind of chemical that you might be exposed to in a different way.
And so I bring this up in the, in the concept of multiple exposures. And so pesticides in combination with other exposures are really important to understand, because at any given moment, we would be exposed to a number of different things. And so understanding how these work individually, understanding how this risk works in combination.
I think gets at [00:13:00] the idea that, you know, we have a really complex array of exposures and that's ultimately what's leading to a lot of of risk for for neurodegeneration. You know, I mentioned this earlier that understanding when exposures are happening is going to be a really critical benchmark for the Parkinson's field, because.
Right now, we have very, very little ways of understanding and knowing when a person is exposed to something. And so as detection methods get better, we may be able to intervene a lot earlier. And I think that that's a really critical area of research. And then, lastly, I think, you know, better understanding mechanisms, really trying to get at modeling experimentally how these toxin exposures occur in human populations is a really critical factor. So, for example, my labs really heavily focused on inhalation exposure, which is really important because this is probably the way most of us are exposed to these [00:14:00] toxicants that are associated with Parkinson's risk. And as you, you might imagine, inhalation has a specific type of toxic risk for the brain.
It causes chemicals to go potentially directly into the brain and foregoing hepatic metabolism in the liver and that can really limit detoxification. And this might be one of the reasons why it's been so hard to translate animal models to human models, because the route of exposure is difficult to replicate.
So, I would say those are really kind of the, the major areas that we're kind of working on that. I think we need to expand on and might get us to an answer you know, in the coming years.
[00:14:38] Prof. Tiago Outeiro: Yeah. And just just thinking about exposure. I mean, one can think that through the eyes or, or through the gut, right? When we eat , all these and this food products that may be also contaminated. And also thinking in terms of the, the gut to brain transmission of pathology.
So is this something you're, you're also interested [00:15:00] in, in studying how pesticides in the gut may trigger, for example, alpha synuclein aggregation and spreading? Is that an area of interest at the moment?
[00:15:10] Dr. Briana de Miranda: Yes, it's definitely something that's being studied. My lab has has looked at microbiome changes in response to ingestion exposures. Other labs have looked more specifically at alpha synuclein accumulation from ingestion exposures and showing that, you know, you can certainly get changes in the gut that are similar to what we might expect to see in people who have idiopathic Parkinson's.
And so this idea that. These systemic chemicals cause Parkinsonian pathology outside of the brain. That's consistent with, with what we see with the idiopathic diseases is absolutely spot on. And I think it's something that we are just beginning to understand, but certainly you know, you would imagine if you're exposed to something, it affects every cell in the body, not just dopamine neurons.
And so [00:16:00] how these systemic exposures can influence gut microbiome spreading from gut to brain various other kind of, you know, you can imagine origins of pathology. I think are, are all really critical in the environmental exposure space. And those studies are beginning to be conducted experimentally.
And I think that those will be really informative.
[00:16:21] Prof. Tiago Outeiro: Right. Yeah. So it seems that we're, we're doing a lot and basic science will continue to bring us more answers . So Brianna, anything else you would like to highlight for our listeners today?
[00:16:33] Dr. Briana de Miranda: I think one thing that is really great is this interest in the idea that environmental risk factors are a strong feature of idiopathic Parkinson's risk. And I'm really grateful to see this topic being a little bit more centered in the, in the Parkinson's field. And I think that as we continue to focus on this and really fund it in a way that is aligned with with the sort of general ideas of [00:17:00] Parkinson's we'll be able to understand that risk a lot better.
And so I'm really encouraged by what I'm seeing with this. And I think there's, there's much more to come. And I think that we're. We're just on the cusp right now of, of understanding these environmental risk factors and we can do a lot better when we have a lot more. So I think that that's, that's kind of my kind of lasting, idea for where to take this.
[00:17:23] Prof. Tiago Outeiro: Great. So Briana, it was a, a pleasure having you on the podcast. Thank you so much for your time and for talking to us and explaining where we are and what, what you and, and now the colleagues are doing in this field. So thank you so much. I really appreciate.
[00:17:38] Dr. Briana de Miranda: Thank you for having me.
[00:17:40] Prof. Tiago Outeiro: So we have just interviewed Dr. Briana de Miranda on the relationship between pesticides and solvents and Parkinson's disease. And I thank you all for listening and I invite you to join us again in our upcoming podcasts. [00:18:00]