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Tag: malaria

Type I interferons induce guanylate-binding proteins and lysosomal defense in hepatocytes to control malaria

Donna Huber on March 25, 2025

Plasmodium parasites undergo development and replication within hepatocytes before infecting erythrocytes and initiating clinical malaria. Although type I interferons (IFNs) are known to hinder Plasmodium infection within the liver, the underlying mechanisms remain unclear. Here, we describe two IFN-I-driven hepatocyte antimicrobial programs controlling liver-stage malaria. First, oxidative defense by NADPH oxidases 2 and 4 triggers a pathway of lysosomal fusion with the parasitophorous vacuole (PV) to help clear Plasmodium. Second, guanylate-binding protein (GBP) 1-mediated disruption of the PV activates the caspase-1 inflammasome, inducing pyroptosis to remove infected host cells. Remarkably, both human and mouse hepatocytes enlist these cell-autonomous immune programs to eliminate Plasmodium, with their pharmacologic or genetic inhibition leading to profound malarial susceptibility in vivo. In addition to identifying IFN-I-mediated cell-autonomous immune circuits controlling Plasmodium infection in the hepatocytes, our study also extends the understanding of how non-immune cells are integral to protective immunity against malaria.

Camila Marques-da-Silva, Clyde Schmidt-Silva, Carson Bowers, Nana Appiah Essel Charles-Chess, Cristina Samuel, Justine C Shiau, Eui-Soon Park, Zhongyu Yuan, Bae-Hoon Kim, Dennis E Kyle, John T Harty, John D MacMicking, Samarchith P Kurup. Cell Host Microbe. 2025 Mar 25:S1931-3128(25)00091-5. doi: 10.1016/j.chom.2025.03.008.

Stereospecific Resistance to N2-Acyl Tetrahydro-β-carboline Antimalarials Is Mediated by a PfMDR1 Mutation That Confers Collateral Drug Sensitivity

Donna Huber on January 14, 2025

Half the world’s population is at risk of developing a malaria infection, which is caused by parasites of the genus Plasmodium. Currently, resistance has been identified to all clinically available antimalarials, highlighting an urgent need to develop novel compounds and better understand common mechanisms of resistance. We previously identified a novel tetrahydro-β-carboline compound, PRC1590, which potently kills the malaria parasite. To better understand its mechanism of action, we selected for and characterized resistance to PRC1590 in Plasmodium falciparum. Through in vitro selection of resistance to PRC1590, we have identified that a single-nucleotide polymorphism on the parasite’s multidrug resistance protein 1 (PfMDR1 G293V) mediates resistance to PRC1590. This mutation results in stereospecific resistance and sensitizes parasites to other antimalarials, such as mefloquine, quinine, and MMV019017. Intraerythrocytic asexual stage specificity assays have revealed that PRC1590 is most potent during the trophozoite stage when the parasite forms a single digestive vacuole (DV) and actively digests hemoglobin. Moreover, fluorescence microscopy revealed that PRC1590 disrupts the function of the DV, indicating a potential molecular target associated with this organelle. Our findings mark a significant step in understanding the mechanism of resistance and the mode of action of this emerging class of antimalarials. In addition, our results suggest a potential link between resistance mediated by PfMDR1 and PRC1590’s molecular target. This research underscores the pressing need for future research aimed at investigating the intricate relationship between a compound’s chemical scaffold, molecular target, and resistance mutations associated with PfMDR1.

Emily K Bremers, Joshua H Butler, Leticia S Do Amaral, Emilio F Merino, Hanan Almolhim, Bo Zhou, Rodrigo P Baptista, Maxim Totrov, Paul R Carlier, Maria Belen Cassera. ACS Infect Dis. 2025 Jan 14. doi: 10.1021/acsinfecdis.4c01001.

 

ANTI-MALARIAL ACTIVITY OF AMENTOFLAVONE ISOLATED FROM LEAF OF CALOPHYLLUM TOMENTOSUM WEIGHT

Donna Huber on October 14, 2024

Calophyllum tomentosum belonging to Clusiaceae family is an Indian medicinal plant used as folklore medicine to cure various kinds of diseases reported in Ayurveda, and the leaves of the plant are also used as an active ingredient for the preparation of a botanical medicine known as ‘Punnaga’, ‘Surapunnaga’ and ‘Tamoil’ among other common names. Chemical profiling of the methanol extract of the defatted leaf revealed the presence of amentoflavone as one of the constituents along with coumarins, terpenoids, steroids, and apetalic acids. Structural determination of these amentoflavone has been conducted by chemical, spectral, and spectrometric methods in comparison with spectral values available in the literature and confirmed by a single crystal X-ray diffraction study. Amentoflavone (1) and its derivative (2-5) tested to check the efficacy of anti-malarial activity against Plasmodium falciparum. Amongst them, only tetra methoxy amentoflavone, (2) exhibited moderate anti-malarial activity with IC50 value 1.99 ± 0.42 µM against Plasmodium falciparum in comparison with artemisinin as control, whereas the other products possessed almost negligible activity although their structural skeletons are identical with little variation of number and nature of substituents. The structure activity relationship (SAR) of the active constituent and its derivatives is reported herein.

Ajoy Kumar Bauri, Joshua H Butler, Maria B Cassera, Sabine Foro. Chem Biodivers. 2024 Oct 14:e202401576. doi: 10.1002/cbdv.202401576.

Researchers discover malaria gene needed to make pair of invasion organelles

Donna Huber on October 2, 2024

by Donna Huber

Vasant Muralidharan and his research group at the University of Georgia’s Center for Tropical and Emerging Global Diseases have uncovered the role of an essential protein in Plasmodium falciparum, the parasite that causes the deadliest form of malaria. The discovery offers new insights for vaccine and drug development.

The parasite that causes malaria was discovered more than 125 years ago, but much is still unknown about this complex, single-celled organism. Researchers in the University of Georgia’s Center for Tropical and Emerging Global Diseases, however, have uncovered the role of one of the parasite’s essential proteins, offering new insights for vaccine and drug development.

Plasmodium falciparum causes the deadliest form of malaria, a disease the World Health Organization estimates killed more than 600,000 people worldwide died in 2022. A large majority of those deaths were children under the age of 5.

Historically, the parasite has been difficult to study due to its complex lifecycle, which includes three stages. One occurs in the mosquito, while the liver and blood stages take place in humans. The blood stage is when the infected person exhibits symptoms of malaria.

In the blood stage, the parasite invades red blood cells (RBCs) where they replicate and can be transmitted to the mosquito. The receptor-ligand complexes that enable RBC invasion have been well-studied and it is one of the targets of anti-malarial vaccines currently in clinical trials. But questions still remain.

“How does the parasite know it has encountered a red blood cell?” asked Vasant Muralidharan, associate professor in Franklin College’s Department of Cellular Biology and leader of the Muralidharan Research Group, where the study took place.

Interested, the team took a closer look at a protein called RON11, which is sent to a pair of unique club-shaped secretory organelles known as the rhoptry (Greek for club) that houses proteins needed to invade the RBC.

Click play to listen to an excerpt of Vasant Muralidharan discussing the cellular mechanics of malaria infection.

“When we knocked out this protein, we found that the parasite could do everything it usually does – create a putative pore in the membrane of the RBC, send proteins needed for parasite invasion through this putative opening into the RBC – but the parasite itself cannot enter the red blood cell,” Muralidharan explained. “If a parasite cannot enter the red blood cell, the life cycle is interrupted and the parasite dies.”

And then things got really interesting.

“We found that the parasites lacking RON11 were only producing half the rhoptry proteins, which are used in invasion,” Muralidharan said.

While it is known that Plasmodium parasites have two rhoptry organelles, they are so teeny-tiny they have been relatively understudied due to a lack of proper tools. However, new tools and techniques are emerging. David Anaguano, a cellular biology graduate student who led the study, traveled on a Daniel G. Colley Training in Parasitology fellowship to the Absalon Laboratory at Indiana University School of Medicine to learn a new tool known as Ultrastructure Expansion Microscopy.

Vasant Muralidharan is an associate professor in Franklin College’s Department of Cellular Biology. (Photo by Lauren Corcino)

“Electron microscopy is labor intensive, and since it uses thin slices of the parasite you are never sure if what you’re looking for really isn’t there or just not in the slice of the sample you have,” Muralidharan said. “Expansion microscopy is like using light microscopy but with a special gel to expand the cell proportionately in all directions. Thus, you don’t get the distortion you would with just an enlarged cell and you can image the entire infected cell in all dimensions. It has been a real game changer.”

As reported in the PLoS Biology paper, the Muralidharan group generated for the first time a Plasmodium cell with only one rhoptry organelle when they removed RON11 from malaria parasites.

“It’s not unusual for an organism to have a backup copy, but we can see that the parasite can create the first rhoptry just fine – without defect – but the second one that should form during the end of the replication cycle never forms,” Muralidharan said. “Why is that?”

As it appears that this second rhoptry is needed for RBC invasion, understanding the mechanisms that control its development could open up new targets for vaccine and drug treatment discovery as well as answering crucial questions like whether the two rhoptries are identical.

“This has been a long unanswered question,” Muralidharan said. “Now with this RON11 knockout parasite that doesn’t form a second rhoptry, we have the tools to answer it.”

Optimization of diastereomeric dihydropyridines as antimalarials

Donna Huber on June 18, 2024

The increase in research funding for the development of antimalarials since 2000 has led to a surge of new chemotypes with potent antimalarial activity. High-throughput screens have delivered several thousand new active compounds in several hundred series, including the 4,7-diphenyl-1,4,5,6,7,8-hexahydroquinolines, hereafter termed dihydropyridines (DHPs). We optimized the DHPs for antimalarial activity. Structure-activity relationship studies focusing on the 2-, 3-, 4-, 6-, and 7-positions of the DHP core led to the identification of compounds potent (EC50 < 10 nM) against all strains of P. falciparum tested, including the drug-resistant parasite strains K1, W2, and TM90-C2B. Evaluation of efficacy of several compounds in vivo identified two compounds that reduced parasitemia by >75 % in mice 6 days post-exposure following a single 50 mg/kg oral dose. Resistance acquisition experiments with a selected dihydropyridine led to the identification of a single mutation conveying resistance in the gene encoding for Plasmodium falciparum multi-drug resistance protein 1 (PfMDR1). The same dihydropyridine possessed transmission blocking activity. The DHPs have the potential for the development of novel antimalarial drug candidates.

Kurt S Van Horn, Yingzhao Zhao, Prakash T Parvatkar, Julie Maier, Tina Mutka, Alexis Lacrue, Fabian Brockmeier, Daniel Ebert, Wesley Wu, Debora R Casandra, Niranjan Namelikonda, Jeanine Yacoub, Martina Sigal, Spencer Knapp, David Floyd, David Waterson, Jeremy N Burrows, James Duffy, Joseph L DeRisi, Dennis E Kyle, R Kiplin Guy, Roman Manetsch. Eur J Med Chem. 2024 Jun 18:275:116599. doi: 10.1016/j.ejmech.2024.116599.

The influence of oviposition status on measures of transmission potential in malaria-infected mosquitoes depends on sugar availability

Donna Huber on May 23, 2024

Background: Like other oviparous organisms, the gonotrophic cycle of mosquitoes is not complete until they have selected a suitable habitat to oviposit. In addition to the evolutionary constraints associated with selective oviposition behavior, the physiological demands relative to an organism’s oviposition status also influence their nutrient requirement from the environment. Yet, studies that measure transmission potential (vectorial capacity or competence) of mosquito-borne parasites rarely consider whether the rates of parasite replication and development could be influenced by these constraints resulting from whether mosquitoes have completed their gonotrophic cycle.

Methods: Anopheles stephensi mosquitoes were infected with Plasmodium berghei, the rodent analog of human malaria, and maintained on 1% or 10% dextrose and either provided oviposition sites (‘oviposited’ herein) to complete their gonotrophic cycle or forced to retain eggs (‘non-oviposited’). Transmission potential in the four groups was measured up to 27 days post-infection as the rates of (i) sporozoite appearance in the salivary glands (‘extrinsic incubation period’ or EIP), (ii) vector survival and (iii) sporozoite densities.

Results: In the two groups of oviposited mosquitoes, rates of sporozoite appearance and densities in the salivary glands were clearly dependent on sugar availability, with shorter EIP and higher sporozoite densities in mosquitoes fed 10% dextrose. In contrast, rates of appearance and densities in the salivary glands were independent of sugar concentrations in non-oviposited mosquitoes, although both measures were slightly lower than in oviposited mosquitoes fed 10% dextrose. Vector survival was higher in non-oviposited mosquitoes.

Conclusions: Costs to parasite fitness and vector survival were buffered against changes in nutritional availability from the environment in non-oviposited but not oviposited mosquitoes. Taken together, these results suggest vectorial capacity for malaria parasites may be dependent on nutrient availability and oviposition/gonotrophic status and, as such, argue for more careful consideration of this interaction when estimating transmission potential. More broadly, the complex patterns resulting from physiological (nutrition) and evolutionary (egg-retention) trade-offs described here, combined with the ubiquity of selective oviposition behavior, implies the fitness of vector-borne pathogens could be shaped by selection for these traits, with implications for disease transmission and management. For instance, while reducing availability of oviposition sites and environmental sources of nutrition are key components of integrated vector management strategies, their abundance and distribution are under strong selection pressure from the patterns associated with climate change.

Justine C Shiau, Nathan Garcia-Diaz, Dennis E Kyle, Ashutosh K Pathak. Parasit Vectors. 2024 May 23;17(1):236. doi: 10.1186/s13071-024-06317-2.

Trainee Spotlight: Grace Vick

Donna Huber on May 16, 2024

My name is Grace Vick and I am a 4th year infectious diseases PhD candidate in Vasant Muralidharan’s lab. I’m originally from North Carolina and received my Bachelor’s of Science in Biology from Western Carolina University. After graduating undergraduate, I completed an internship at the Defense Forensic Science Center doing forensic biology research. After that, I spent 2 years as an ORISE Fellow at the Centers for Disease Control and Prevention, studying and identifying genetic markers of multi-drug resistant strains of Neisseria gonorrhoeae. I came straight to UGA through the ILS program after my fellowship at CDC.

What made you want to study science?

Ever since I was little, I’ve always spent a lot of time being outside in nature and enjoyed figuring out the intricacies of how things work. During my undergraduate, I was able to explore the different areas of science and found the molecular biology of genetics to be an interesting field that is highly translatable and still vastly unknown. After I spent a few years gaining lab experience and an appreciation for the public health concerns of infectious diseases at the CDC, I knew I wanted to pursue a PhD in that field which brought me to UGA.

Why did you choose UGA?

My experience at the CDC offered the opportunity to learn about diseases and public health issues across all sectors and countries, which led me to learn more about parasitic diseases. Previously, I knew nothing about these diseases but as I learned more about their complex and fascinating life cycles and how these diseases of poverty impact people around the world, I was captivated by this research. Because I was really interested in spending my PhD studying infectious and parasitic diseases, I found out about the CTEGD at UGA and that is what brought me here. The CTEGD is a really wonderful environment for trainees to be exposed to exciting and diverse parasitology research, and I’ve really enjoyed my experience here.

What is your research focus and why did you choose it?

Our lab works on the deadliest form of malaria, Plasmodium falciparum. P. falciparum kills over half a million people each year, with the majority of those deaths being children under the age of 5. Our lab is interested in understanding the molecular mechanisms that are essential to asexual blood stage of this parasite. My work specifically focuses on determining the role of previously unknown proteins that we have discovered are essential for asexual stage invasion of merozoites into host red blood cells. Using a combination of genetic engineering, molecular, and cellular biology techniques, I aim to determine the molecular function of these proteins in the human asexual stage invasion of red blood cells.

Have you received any awards or honors?

In addition to receiving the NIH T32 Predoctoral Fellowship, I have been invited to present at multiple national and international conferences such as Molecular Parasitology Meeting in Massachusetts and Molecular Approaches in Malaria in Lorne, Australia where I won a poster award.

What are your career goals?

When I graduate with my doctoral degree, I hope to either join governmental research or the industry sector. If I decided to head into governmental work, I would choose a career at the CDC where I could continue working in the parasitology research field and apply current public health policies to the international parasitology field. If I decide to join the biomedical industry sector, I would want to work in Research and Design at a company that designs therapeutics and diagnostics for disease prevention and treatment.

What do you hope to do for your capstone experience?

I would really love to experience fieldwork in a malaria-endemic region. I think having the experience of meeting people and learning firsthand how this disease affects millions of people every day would be very eye-opening for me since I have only seen the lab side of malaria. The ability to experience fieldwork would give me a broader experience with how malaria is researched and treated outside of the lab environment and in rural lab environments. I would love to visit Africa or South East Asia to conduct fieldwork in a malaria-endemic environment.

What is your favorite thing about Athens?

Obviously, I love the food in Athens! I love going downtown to grab food and drinks on the weekend. Otherwise, I enjoy getting out and exploring the green spaces and parks that Athens has to offer such as Sandy Creek and the North Oconee Greenway with my husband and dog.

Any advice for a student interested in this field?

I would say the best advice is to read and soak up as much as you can about parasitology both before you get into the field and after. A lot of research has overlap between different parasites and it’s helpful to know about other parasitic diseases that might not be your main focus. Plus, parasites are fun! 🙂 My other advice in general for starting graduate school is to always reach out to students in labs you’re interested in joining. Students are pretty much always willing to help give clear insight into lab dynamics, mentorship of the PI, and generally how life working in that lab is. That information is all really helpful to know when choosing which lab to join!

 

Support trainees like Grace by giving today to the Center for Tropical & Emerging Global Diseases.

Hepatocytes and the art of killing Plasmodium softly

Donna Huber on May 6, 2024

Figure 1. The gap in our understanding of how hepatocytes eliminate Plasmodium.

 

The Plasmodium parasites that cause malaria undergo asymptomatic development in the parenchymal cells of the liver, the hepatocytes, prior to infecting erythrocytes and causing clinical disease. Traditionally, hepatocytes have been perceived as passive bystanders that allow hepatotropic pathogens such as Plasmodium to develop relatively unchallenged. However, now there is emerging evidence suggesting that hepatocytes can mount robust cell-autonomous immune responses that target Plasmodium, limiting its progression to the blood and reducing the incidence and severity of clinical malaria. Here we discuss our current understanding of hepatocyte cell-intrinsic immune responses that target Plasmodium and how these pathways impact malaria.

Camila Marques-da-Silva, Clyde Schmidt-Silva, Samarchith P Kurup. Trends Parasitol. 2024 May 6:S1471-4922(24)00086-2. doi: 10.1016/j.pt.2024.04.004.