Silvia Moreno and her research team at the University of Georgia’s Center for Tropical & Emerging Global Diseases and Department of Cellular Biology provided evidence that it is possible to develop a drug combination that acts synergistically by inhibiting host and parasite enzymes in a recently published article in Antimicrobial Agents and Chemotherapy.
What is toxoplasmosis?
Toxoplasmosis is caused by the pervasive intracellular Apicomplexan parasite Toxoplasma gondii. The parasite is found throughout the world and can infect humans and a number of animal species. In the U.S., people may contract it by consuming undercooked meats, especially pork, lamb, venison, or through contact with contaminated cat feces.
Human infections are usually asymptomatic but the parasite can persist in the form of tissue cysts. It has been estimated that 30–50% of the global population may be chronically infected with Toxoplasma. The immune system of a healthy individual can control the infection, but it can reactivate when there is immunosuppression due to organ transplant, cancer chemotherapy, or in people infected with HIV.
Toxoplasmosis is especially dangerous to the unborn fetus when the mother becomes infected during pregnancy as it can result in miscarriage or stillbirth. Surviving infants can suffer from visual, hearing, motor, cognitive, and other problems.
Some strains of T. gondii can cause severe ocular disease in people with a healthy immune system. Current drug therapies do not prevent disease progression that leads to blindness in ocular toxoplasmosis patients.
Toxoplasmosis represents a serious public health problem and no preventative or therapeutic vaccine is available for humans.
Need for better drug treatments for toxoplasmosis
Drugs presently used against toxoplasmosis do not eradicate chronic infection and as many as half of treated patients do not respond to the therapy. Additionally, a large number of people have an allergic reaction to the current treatment option. Furthermore, some the current drugs have recently become very expensive.
There is a need for safe and effective treatment.
Moreno and her team study the isoprenoid pathway to identify new drug targets. Isoprenoids are lipid compounds with many important functions. One particular step in this pathway has been identified as essential in T. gondii. A drug targeting this pathway could kill the parasite.
Drug combination may provide more effective and less expensive treatment
Moreno’s group proposes a double hit strategy of combining inhibitors of host and parasite pathways as a novel approach against toxoplasmosis. They have found a synergistic effect by combining new and potent sulfur-containing bisphosphonates, as well as other commercially available bisphosphonates, with several statins against a lethal infection of T. gondii using a virulence mouse model.
Bisphosphonates are widely used for the treatment of bone disorders. Previous studies by Moreno and her colleagues have shown that bisphosphonates inhibit the growth of a variety of protozoan parasites like T. gondii. There are a number of commercially available bisphosphonate drugs.
Statins are a class of drugs typically prescribed to lower cholesterol. They work by blocking a particular enzyme known as 3-hydroxy-methylglutaryl-coenzyme A reductase. As with the bisphosphonates, there are already a number of commercially available statins.
Bisphosphonates alone have been very effective when treating a lethal infection of T. gondii in mice. However, Moreno’s team found that combining bisphosphonates with the statin atorvastatin (Lipitor) was almost 3 times more effective under similar conditions of infection and treatment. Additionally, they found very low doses of both drugs could be used for treatment, which would significantly decrease the potential for adverse side effects.
This double hit strategy may be the key to effective treatment because the parasite not only makes its own isoprenoids, but it can also import them from the host. The ability to manipulate the host cell for its own benefit poses a challenge for drug development against toxoplasmosis. Therefore, inhibiting the host from producing this material along with inhibiting the parasite’s ability to create isoprenoids is an interesting and novel strategy for drug development.
Further studies for this novel therapeutic approach needed
This study demonstrates that early treatment is key to the cure of infection with a particular strain of T. gondii for acute infection. Since current treatments often fail to cure chronic infection Moreno and her group will next test this combination strategy in an established chronic infection mouse model.
Furthermore, Moreno predicts that this double-hit strategy of inhibiting both host and parasite pathways will work for other intracellular Apicomplexan parasites, such as the malaria-causing Plasmodium parasite. Additional studies will be needed to test this hypothesis.
An online version of this study is available: Li Z-H, Li C, Szajnman SH, Rodriguez JB, Moreno SNJ. 2017. Synergistic activity between statins and bisphosphonates against acute experimental toxoplasmosis. Antimicrob Agents Chemother 61:e02628-16. https://doi.org/10.1128/AAC.02628-16
Evgeniy’s research focus
Generally, Evgeniy is interested in mechanisms of transmembrane transport and their role in parasite homeostasis. His current project goal is to characterize how the IP3R function modulated within the Trypanosoma brucei, the parasite that causes African Sleeping Sickness, acidocalcisomes where it resides and how deregulation of this process can contribute to cell death. This research topic addresses poorly studied mechanisms of parasite physiology and has the potential importance of discovering new methods of patient treatment.
Each T32 trainee is provided with the opportunity to complete a capstone experience at the end of their fellowship. This experience often involves an extended visit to a collaborator’s laboratory to learn new techniques or to an endemic country to see how their research connects to actions being taken in the field.
“I hope to expand my expertise in both electrophysiology and cellular biology approaches, which will allow me to conduct independent research,” said Evgeniy.
T32 fellowship helps trainee achieve goals
“T32 is a unique possibility to prepare me for an independent research career,” said Evgeniy. “It gives great tools to achieve this goal.”
Malaria is a mosquito-borne disease that has a disproportionate effect in poor and underdeveloped countries without access to western medicine. According to the WHO’s World Malaria Report, there were 212 million new cases of malaria worldwide in 2015 and an estimated 429,000 deaths.
Malaria is caused by the Plasmodium parasite. Plasmodium falciparum is the deadliest of the species infecting humans, causing 50% of all malaria cases. Unfortunately, it has become resistant to current drug treatment.
Belen Cassera and her laboratory group at the University of Georgia have been identifying possible compounds for new antimalarial medication from natural plant sources.
History of anti-malarial drugs
Malaria has long been treated with plant-based medicine. Quinine, which comes from the bark of a cinchona tree, was first isolated as an antimalarial compound in the 1800s, though there is evidence that bark extracts have been used to treat malaria since the 1600s. The cinchona tree is native to Peru.
Quinine was the treatment of choice until the 1940s when other drugs, with fewer side effects, replaced it. One of those drugs was chloroquine, which was discovered in 1934. Following World War II, chloroquine became the preferred treatment for malaria and was prominent in mass drug administration programs of the 1950s. This wide-spread use, in part, led to chloroquine resistant strains of P. falciparum.
The rise of chloroquine-resistance led to the discovery of several potential synthetic alternatives. However, in 1972 Chinese scientists isolated artemisinin from Artemisia annua, commonly known as sweet wormwood. It is native to Asia but has been naturalized in several regions including North America. It has been the main treatment of malaria in south-east Asia. However, in recent years artemisinin resistance has also emerged. (Source: History of Antimalarials)
Cassera in collaboration with David Kingston at Virginia Tech and Michael Goetz and Jason Clement from the Natural Product Discovery Institute (NPDI) has a grant from the National Center for Complementary and Integrative Health (R01 AT008088) to study plants in the NPDI Repository to identify new antimalarial compounds.
Discovering new drugs from plants
In this project, they are concentrating on plants that have not been studied for their anti-malarial properties. Also, they are looking at plants that indigenous people have used to treat the various symptoms associated with malaria.
So far over 28,000 extracts have been screened and the team has identified over 100 compounds with anti-malarial activity.
In recently published findings, the group has reported the discovery of anti-malarial compounds in Malleastrum sp., Crinum firmifolium, and Magnolia grandiflora. The first two are plants found in Madagascar, but the last one is better known as the southern magnolia and can be found in backyards throughout the southeastern United States.
From the southern magnolia extracts, the Cassera and Kingston labs identified two new compounds with anti-malarial activity. It was also discovered that it contained six compounds that have been identified in other plants as possible malaria drug compounds. An online version of the study is available: https://doi.org/10.1002/cbdv.201700209Extracts from Crinum species, which are in the amaryllis family, have been used traditionally to treat ailments including fever, pain management, swelling, sores and wounds, cancer, and malaria. Following success in isolating new anti-malarial compounds from an extract of Crinum erubescens L. F. ex Aiton, they turned to C. firmifolium, which was already in their International Cooperative Biodiversity Group collection. Extracts yielded 4 known compounds and three new compounds with possible anti-malarial activity. It was observed that the potency of several of the compounds against the drug-resistant strain of P. falciparum was approximately the same as their potency against the drug-sensitive strain. An online version of the study is available: https://doi.org/10.1016/j.bmc.2017.06.017
An extract of the wood from a species of Malleastrum in the mahogany family was found to have moderate antimalarial activity against a drug-resistant strain of P. falciparum. The genus Malleastrum (Baill.) J.-F. Leroy is endemic to Madagascar and comprises 20 currently accepted species. However, there appear to be at least four previously unidentified species. The plant material in this study is almost certainly from one of the species that is still waiting to be named and described. An online version of the study is available: https://doi.org/10.1002/cbdv.201700331
Next steps in the drug discovery process
“We have identified some really promising compounds,” said Belen Cassera. “A few could be ready for pre-clinical studies in a few years.”
In addition to testing for anti-malarial activity, the Cassera lab is also looking at the mechanism of action – how the compound works. This is an important step in drug discovery; because once it is understood how the compound works a synthetic analog could be synthesized and manufactured at a cheaper cost and in a safer form.
Each compound they have identified has several molecules associated with it. In their current state, some of these compounds have too high of a toxicity to be considered for potential drug treatment. Therefore, it is important to strip the compound down to only those molecules that have potent antimalarial responses and hopefully they can remove the molecules associated with toxicity. Once this has been accomplished, then matching synthetic molecules can be created in the lab and scaled up for mass production.
Being able to create these synthetic molecules is a necessary step in the drug discovery process. Natural material can be costly to collect or not available in abundance. While the southern magnolia seems to be abundant in the yards of Georgia, its natural range only stretches from coastal North Carolina south to central Florida, and then west to eastern Texas and Oklahoma. In addition, due to environmental differences, many times compounds isolated from a plant from one part of the world cannot be found in the same plant grown in another which reinforces the need to focus on active compounds that can be resynthesized in the lab.
With the appearance of drug-resistant strains of the malaria parasite to all current medications, it is imperative new treatments be discovered. Since plant-based and traditional medicine have yielded a number of drugs historically it is likely that the next treatment option will again come from a plant source. There are countless numbers of plants that have yet to be studied for their anti-malarial uses. Belen Cassera and her team just might find the cure for malaria in your backyard.
Athens, GA–Mosquitoes transmit diseases such as Zika virus, dengue, and malaria to people and other vertebrates worldwide. In a newly funded National Science Foundation (NSF) project, Michael Strand and Mark Brown, both professors in the Department of Entomology and members of the Center for Tropical and Emerging Global Diseases, hope to gain new insights into how hormones coordinate immune responses with reproduction.
The immune and reproductive systems of all animals, including mosquitoes, require large amounts of energy but how these energetic demands are regulated at the molecular level are poorly understood. How immune defenses are regulated relative to other functions like reproduction is of long-standing interest and the main goal of this project is to answer this question.
Mosquitoes provide an interesting system for addressing these issues because almost all species must feed on blood from a vertebrate host, such as humans or another animal, to reproduce. However, blood feeding exposes mosquitoes to microorganisms that cause disease in mosquitoes, the vertebrate hosts mosquitoes feed upon, or both. Background studies by Strand and Brown have shown that certain hormones co-regulate reproduction and immune defense.
“What we hope to characterize in this project are the biochemical pathways these hormones interact with, and how these pathways affect the ability of mosquitoes to defend themselves from infection,” said Strand. “We also will learn whether these pathways function similarly or dissimilarly between species.”
The fundamental questions about reproduction and immunity that this project is designed to answer apply not only to mosquitoes but to all animals. “The information we generate will also potentially provide information that can be applied toward reducing mosquito reproduction and transmission of pathogens that cause human disease,” said Strand.
NSF requires grant recipients to engage in activities that have broader impacts that enhance STEM education and improve science literacy in the general public. “The public at-large generally knows that mosquitoes can transmit human diseases, but people often do not understand how disease transmission occurs or why some mosquito species are disease vectors but most are not,” said Strand. In conjunction with Georgia 4-H and the Cooperative Extension Program at UGA, teaching materials for middle and high school students will be developed that explain disease transmission, the mosquito life cycle, and strategies for controlling vector populations.
National Science Foundation Award #1656236 “Endocrine regulation of immunity and reproduction in mosquitoes”
Writer: Donna Huber
Contact: Michael Strand, Mark Brown
Manuel Fierro is a pre-doctoral trainee in Vasant Muralidharan’s Laboratory. He is originally from Ecuador. His family moved to the US when he was 9 years old, and he has lived in Georgia ever since. Manuel received his Bachelor of Science degree in Cellular Biology from the University of Georgia in 2014. He is a recipient of the Center’s NIH funded T32 Training Grant for Interdisciplinary Parasitology, Vector Biology, and Emerging Diseases.
Manuel’s research focus
Manuel’s project deals with understanding how calcium is regulated in the endoplasmic reticulum of Plasmodium falciparum, the parasite that causes malaria.
“My undergraduate training was in Dr. Silvia Moreno’s lab studying calcium signaling in Toxoplasma gondii and I wanted to answer the same type of questions in Plasmodium,” said Manuel.
Each T32 trainee is provided with the opportunity to complete a capstone experience at the end of their fellowship.
“My home country of Ecuador is approaching elimination of malaria,” said Manuel, “and I would like to work with some of the researchers in the field there who track populations of infected mosquitoes as well as monitor cases of infection in humans.”
T32 Fellowship helps trainee achieve goals
“I truly enjoy working in a lab, but it is not the same as experiencing what diseases are like in the real world,” said Manuel. “This fellowship will help me expand my understanding of malaria by giving me the opportunity to see it in a different setting.”
Manuel is currently considering a career in industry, but he is open to staying in academia.
Support trainees like Manuel Fierro by giving to the Center for Tropical & Emerging Global Diseases
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