Disrupting the Complicated Cycle of Malaria: Caroline Ng Discusses her Work

Richard: Hello, this is Richard Jacobs with the Finding Genius Podcast. My guest today is Caroline who is an assistant professor in the Department of Microbiology. So, Caroline, thanks for coming.

Caroline: Yeah, thanks for having me.

Richard: If you would tell me about your research.

What are you working on?

Caroline: My lab works on malaria and we’re seeking to understand drug resistance mechanisms.

Richard: So malaria, when it gets to people, or is it still in the mosquito?

Caroline: That’s a good question. So malaria is caused by a parasite and this parasite needs two different hosts to survive and to complete its lifecycle. So, as you mentioned, there’s a stage in the mosquito and upon a bite from an infected mosquito, the parasite is transmitted into humans first. The parasite travels to the liver where it establishes a liver stage and then after about two weeks, these parasites get released into the bloodstream where they, in fact, red blood cells and that’s the stage that I study. There are only two asexual blood stages and at some point, these parasites in the blood will receive a signal to commit to sexual differentiation and these sexual forms are then taken up by a mosquito when it bites and infects a human and they can recombine sexually within the mosquito and then the cycle goes on and on.

Richard: What does the parasite look like? Is it a single cell or is it multi-cell? How many of them do people have when they get it?

Caroline: So the parasite is a protozoan. So it’s a single-celled parasite, but it’s a eukaryote, meaning that it has all of the internal organelles that humans always have. So like a nucleus of mitochondria, the Golgi apparatus things like that and it also has an additional organelle called the apicoplast, which is derived from double endosymbiosis of algae a long time ago.

Richard: What is the structure inside of it?

Caroline: Are you asking about the various structures or are you asking about the apicoplast specifically?

Richard: The structure you just mentioned, what are its functions?

Caroline: So it’s important for clean and isoprene oil and fatty acid biosynthesis. It allows the parasite to survive and able to use energy. So the parasite functions in a way that’s similar to humans. So it requires amino acids to make proteins and for example, even in humans, we also have a fatty acid synthesis. So we, for example, all our lipid membranes are made out of phospholipid by years, which are which consist of fatty acids. It also has membranes and so you need these fatty acids.

Richard: So it appears to have many special abilities that cells don’t have and it’s in our blood. Is it literally inside of the red blood cells or is it just in a blood mixture?

Caroline: No, it only invades the red blood cell and so you’re asked about the numbers of the parasite. So when so there are different forms of the parasite and it looks different in the different stages. So when it’s in a mosquito ready to be transmitted to a human, these parasites live in lines of the mosquito and they look like little worms, little fat worms. When they get injected into a human, it first goes into your skin, and then they find a way through into microcapillaries and from their day home into your liver. So they trends migrate through Cooper solids, which are never macrophages and then when they find a suitable host, a suitable parasite, which is a liver cell, they form a vacuole around themselves to protect themselves from the host and so within this cell, this can differentiate and it then multiplies. So that will be released into the bloodstream where each one can infect a red blood cell and then when that infects a red blood cell, it progresses through the blood-stage from rings to trough. So within the asexual reckless cycle, one parasite can produce up to 24 to 32 daughter marazoans and you can see that it’s exponential amplification.

Richard: What happens to the functioning of the red blood cells that have the parasite in them and that are still able to exchange oxygen?

Caroline: I would assume that it’s impaired because when these parasites get into the red blood, so they digest the hemoglobin that’s in the red blood cell.

Richard: So that means that the red blood cells become useless after a time.

Caroline: Yeah. So they have to digest hemoglobin for two reasons. One, as I mentioned, they are just like us and the amino acids to go to build protein and so they digesting the hemoglobin indirectly. So it’s derived amino acids as building blocks for their proteins and they also have to digest it because hemoglobin is the major protein within mature red blood cells and they require the space within the red blood cells. So they have to digest it to create space for themselves.

Richard: What happens when red blood cells don’t divide?

Caroline: They get cleared by the spleen. So that actually really interesting. So parasites have evolved this mechanism of not being cleared by the spleen and so in humans infected with malaria parasites, their red blood cells display this phenomenon called resetting, which means that an infected red blood cell and uninfected red blood cells slump together and parasites also increase to the appearance of the red blood cells that are in, meaning that now these cells are able to stick to the endothelial lining. So the lining of your blood vessels so that they don’t get washed away into the spleen.

Richard: What happens after they’re infected? Do they then go to the screen?

Caroline: So the release of parasites also releases all these debris and that’s what causes the classical symptoms of malaria, which is fever.

Richard: But wouldn’t people get clots on small capillaries in places like that?

Yeah, you can. So there’s a range of symptoms of malaria. So when you get infected, you can just get mild symptoms where you feel malaise and you have these characteristics, cyclical fevers, and chills. But it can also be really severe and if you have a lot of parasites in your blood, that’s exactly what happens. So basically in your micro capillaries within your organs, it can cause organ failure. So you can start having, for example, cerebral malaria or you can have a sense of malaria and these are complications from basically locking. I mean, that’s one of the reasons is it’s complicated.

Richard: How long does it take? How long is this infection stretch or when it gets into the blood?

Caroline: There’s a couple of questions in it. So each different parasite strains have different timings. But in general, so some of them are most of the falciparum strains. I work with are on a 48-hour cycle. But it can range depending on the parasite strain.

Richard: So you said that when it affects red blood cells, they’ll eat them and more and more accumulate until there’s suddenly a signal where they get to change their way of doing things. What does that signal and what happens?

Caroline: So the signal there’s a couple of things that that signal that so nutrient deprivation can cause them to commit to sexual differentiation sometimes and too many other drugs cause that and it’s a switch on one of the genes in the Plasmodium parasite itself.

Richard: So what happens when they go to the sexual stage?

Caroline: So it has to happen in people so they replicate asexually within the blood, multiplying every 48 hours, and then when they commit to sexual differentiation, they actually decide right early on when they invade. That’s when the commitment already starts. So when they invade, they become rings and marazoans are released and the interesting thing is that we see that this commitment happens in the ring stages. So in the first stage and so once it invades, it knows it’s actually going to become a Komeido site, which is the sexual stages and there are female and male Komeido sites and these will just be in your blood and then when a mosquito happens to bite, you take up parasites. That happens to be Komeido sites and these sexual forms can then recombine into them into mosquito.

Richard: For people who are infected, more attractive to mosquitoes. has anyone studied whether they’re giving off pheromones or other chemical signals that attract mosquitoes to them more than others?

Caroline: So I read a study that showed that mosquitoes in the jungle prefer biting animals, but mosquitoes in urban areas prefer biting humans. Only female mosquitoes bite and they only feed when they are pregnant. So when they have babies, when they have eggs, that’s when they feed on blood.

Richard: What aspect of malaria are you trying to figure out?

Caroline: So there are five species of plasmodium that cause malaria in humans and of that five plasmodium falciparum is the most virulent, and it causes the most number of deaths. It’s very prevalent in Africa. But it’s also found in Asia and South America and the thing about these parasites is that we have lots of antimalarial drugs and our first line of drug treatment at the moment is artemisinin-based combination therapies. So this is a very potent drug called artemisinin. But these drugs are short-lived and so they need to be partnered with a longer-lasting drug. So to make sure that all the parasites are cleared from your body and unfortunately, what we’ve been seeing in Southeast Asia is that there has been a decrease in the ability of these drugs, these artemisinin, to clear parasites. So there’s a delayed parasite clearance. So we are worried because we’ve lost other drugs before due to parasite drug resistance and we’re worried that this is a signal that this is the beginnings of drug resistance to artemisinins. So what my lab and what other labs around the world are really trying to understand is what’s causing this artemisinin resistance and if we can understand that, we can then start to design drugs that either synergize that that work together with that pathway or to sort of finding an Achilles heel in the parasite so that we don’t lose is very, very important drug.

Richard: So what is the resistance look like, these little malarial drugs you’re talking about? What’s the mechanism of action? What is the resistance look like? How can you tell that someone’s malaria is resistant to their drug designs, which is actually better?

Caroline: Yeah. That’s actually how you tell us. So for other drugs. So, for example, chloroquine was used as an entry when they are over a very long time and it’s still used in certain parts of the world where there isn’t resistance to chloroquine. But for many, many parts of the world, there are chloroquine-resistant parasites and so that drug is essentially useless in those regions and basically, that means that if you have a chloroquine-resistant parasite, if you treat with chloroquine, the parasite still remain in your body and you will continue to be sick for that. We know that chloroquine inhibits a process and the parasite.

So when parasites digest hemoglobin, heem is released and it is really toxic to parasites and to all organisms and so what they need to do is detoxify that heem and chloroquine inhibit the detoxification process and for that resistance to chloroquine, for example, is rendered by mutations in a transporter in the malaria parasite that transports the drug out of the out of the digestive tract so that the drug can no longer interfere with this process. So that’s pretty straightforward because there’s one gene that’s involved, multiple mutations that gene confers resistance. Now for artemisinin resistance, we’re still trying to figure that out. So and we still don’t really know how it kills the parasite. But there are several theories. So it seems that when so artemisinin is just a really beautiful drug. It actually acts like a prodrug. So the key moiety of this compound is an endoperoxide branch and when the drug gets into the parasite, as I mentioned, the parasite digests hemoglobin and heem is released and now the drug is active and so basically you can see a differential potency of this drug. So it’s very specific for hemoglobin digesting parasites.

Richard: So what do you say makes heem toxic? Is it because it’s very iron-rich with iron and hemoglobin is what makes it toxic?

Caroline: So it’s toxic because it’s very reactive. So in the iron there are unpaired electrons in that molecule and so it’s very reactive and all those cause reactive oxygen species to accumulate and that’s not good for ourselves.

Richard: So what does the parasite do? Does it package to heem like separate vacuoles, isolated or what does it do, and how does the heem get out of the body?

It doesn’t get out. So heem is released through hemoglobin digestion, the heem is converted into a different form and then it basically gets polymerization and so it gets packaged into this form that is now inert and actually, way before they even knew that malaria was caused by parasites, they could see this pigment. You can see this yellow pigment under a light microscope and they call this the malaria pigment. So now we know it’s hemazoans.

Richard: So what happens if this builds up inside the blood vessels? Where does it build up?

It would be within the digestive bascule of the parasite. But basically, this hemoglobin is in there. It doesn’t do anything. OK. So to answer your earlier question, so heem will activate artemisinin or artemisinin like compounds and that basically allows non-specific calculation of parasite proteins and we think that because you now have this additional group, an additional chemical group on proteins that hinders the ability of these proteins to function properly and that’s how we think the parasites die.

Richard: Is chloroquine administered with artemisinin and does it help?

Caroline: No, they’re separate. Sorry, I just brought that up to show that we used to have a really good drug and there’s resistance and now we can’t use it. So we don’t want that to happen with artemisinin and you asked me about what is the clinical manifestations of artemisinin resistance? So if a parasite is sensitive to the drug, the parasites will be cleared within three days and if it’s not, if the parasites will remain after three days, you can take a blood smear. You can take a blood sample from a patient and look at that under the microscope and you’ll be able to see, are their parasites and if there are, then you know that these parasites are resistant to the drug. So eventually they do get cleared. I would like to make that known. Eventually, they do get cleared and there haven’t been any deaths from artemisinin-resistant malaria.

Richard: What happens in the normal course of malaria if it can’t be treated? The parasites build up and build up and starve the person of the ability to carry oxygen to their cells and kill them?

Caroline: Yes. Sometimes you can die. So it depends on your immunity. So someone’s immune system can control it.

If you are able to control it, then it will. You can eliminate these parasites. But if you’re unable to eliminate them, then it can be severe and lethal.

Richard: Are there therapies where you take the person’s blood and pass it through an external filter and then put it back into their body and then you know what the filter is comprised of. Let’s say it has chloroquine embedded in it or some other compound. Are there any therapies like that where since they reside in the red blood cells, perhaps there are therapies like that?

Caroline: No, we don’t we don’t think about those therapies. So one of the things we think about, we try to keep in mind when we develop antimalarial therapies is that most of the burden of malaria occurs in countries that are the poorer and so what’s really important is that each dose of antimalarial therapy has to be less than a dollar, and even then it’s quite unaffordable and so if you’re talking about taking blood and terrify, I mean, it will work for scientific reasons, but also if that process is too expensive. You need cheap therapy because it, unfortunately, is ravaging countries that are not very rich. So you can’t think of expensive therapy.

Richard: What are your near-term goals for your research in the next couple of years? What big questions do you want to answer?

Caroline: So we would really like to contribute to the communities, the scientific community’s understanding of what is causing that artemisinin resistance because it’s not quite pinned down and we’re looking to develop some new therapies are uncompromised by existing resistance mechanisms. So that’s really important because if parasites are already resistant to a certain mechanism, they can sometimes be resistant to a drug that they’ve never seen. So we call this cross-resistant and it’s quiet you can imagine that’s quite problematic. So you don’t want to spend all this time and money. I think it’s something like it takes a billion dollars and 10 years to develop a drug. So you don’t really want to spend all that time if you if at the end of the day, it’s just going to fail in the real world. So what I see my not contributing is how do we lay the foundation on the basic science side of trying to understand how do these parasites gain resistance and what sorts of mechanisms are involved and then how do we find drugs that don’t target these mechanisms or we can exploit these pathways to develop even more potent drugs.

Richard: What’s the best way for people to find out more and get in contact with your lab and where you are?

Caroline: You can find me on the UNMC Web site. If you search for UNMC Caroline Ng, you can find me or you can. I also have a Twitter and Instagram page which admittedly I don’t update a lot. That’s lab_malaria for both of them. Yes and if anyone has any questions, I’d love to chat with them.

Richard: Thanks for coming. I really appreciate it.

Caroline: Yeah, no problem. Thanks for this interview.