CLEMSON -- Clemson University scientist Cheryl Ingram-Smith has been awarded a three-year, $424,000 grant from the National Institutes of Health (NIH) to study the inner workings of a parasite that causes 50 million cases of amoebic dysentery each year and kills 50,000 to 100,000.
Entamoeba histolytica, an amoeba that is found worldwide, causes amebiasis, a parasitic infection of the intestines. About 50 million people get dysentery from the infection. Another 450 million who become infected do not develop this form of dysentery but are still carriers of the disease and can contribute to its spread. In rarer cases, the parasite can move to the liver and cause death if left untreated.
Entamoeba histolytica is most prevalent in developing nations and may also be a problem in those undergoing civil unrest where barriers between human feces and food and water supplies are inadequate. It is not considered a serious threat to nations like the United States where sanitation standards suppress the pathogen's ability to spread.
Ingram-Smith has been studying the microscopic parasite for several years. The NIH grant will accelerate her efforts by funding the purchase of new equipment and supplies and also by paying the salaries of full-time graduate research assistants. Ingram-Smith's team will focus its research on a pair of unusual enzymes that the parasite uses to overcome its lack of the energy-producing processes that fuel the cells of most animals and plants.
"Entamoeba histolytica is an amoeba, so it just kind of oozes around. It's actually fun to watch under the microscope," said Ingram-Smith, assistant professor in Clemson's genetics and biochemistry department. "But its metabolism is really unusual. Most organisms can make their own building blocks. But Entamoeba species lack many of the metabolic pathways that are typically found in cells. Most eukaryotes (cells containing membrane-bound compartments) are able to convert glucose into energy very efficiently. But though Entamoeba's cells are eukaryotes, they lack mitochondria, which are the power generators of most cells. Thus, they have to find other ways to make sufficient amounts of energy to thrive."
One way the amoeba compensates for its deficiencies is by devouring the cells of its host, which contain many of the compounds necessary for survival, such as amino acids and nucleic acids.
"We eat meat, they eat cells. And that's where they get a lot of the materials they need," said Ingram-Smith, who in addition to this NIH grant is also one of the investigators for a recently announced $10.5 million NIH grant focused on fighting organisms responsible for infectious diseases. "But the Entamoeba don't derive enough energy from just eating cells. They still need more. That's where the enzymes we're studying enter the equation."
Through a series of pathways, cells with mitochondria generate 30-32 adenosine triphosphates (ATPs) per unit of glucose. ATPs, which are often called the "molecular units of currency," transport chemical energy within cells and are vital for growth and replication. However, since Entamoeba lack mitochondria, they can't break down glucose nearly as well as other cells. Entamoeba can only use one of the pathways, called glycolysis, which is the enzymatic breakdown of a carbohydrate. Glycolysis normally produces just two ATPs per unit of glucose.
"We're studying a couple of enzymes that we think help glycolysis work better within the parasite," Ingram-Smith said. "One of the enzymes I'm working on enables the amoeba end up with five ATPs instead of two. Compared to mitochondria, this still isn't much. You're talking minimum wage versus a CEO's salary. But two to five is still a relatively large increase. The second enzyme we're studying may help the parasite ramp up glycolysis even further."
When outside the human body, the amoebas are encased in a tough, protective cyst. Once ingested, the cysts help them survive their journey through their host's acid-laden stomach until they reach the upper intestines, where they cast off the cysts and begin to feed and replicate. Eventually, they settle in the lower intestines.
Current medicines are effective in preventing death, but their availability is severely limited in many parts of the world.
"Countries where this is most prevalent don't usually have sufficient or readily accessible medical facilities," Ingram-Smith said. "More importantly, Entamoeba causes 50 million cases of dysentery every year. Even though the recovery time is usually only one to two weeks, when you're talking tens of millions of people, you're talking a potentially huge economic impact in certain areas of the world."
Though Entamoeba kills only a small percentage of the people who become infected, the NIH still lists it as a potential agent of bioterrorism.
"If a large part of a nation's population is sick from dysentery, you can seriously cripple its operational abilities," Ingram-Smith said. "Is Entamoeba being used like this now? Not to anyone's knowledge. But there is that potential, because it's something that can easily get into a water system by various means. And if you're having problems with your water system breaking down because of wars, it would not be difficult for an enemy to spread the parasite and wreak havoc."
Thus far, two graduate students have played significant roles in Ingram-Smith's research:
* Thanh Dang - who was born in Vietnam but who grew up in Baton Rouge, Louisiana, after his family immigrated there - is a fourth-year graduate student in Clemson's biochemistry and molecular biology Ph.D. program. Dang received a Bachelor of Science degree in microbiology in 2009 from Louisiana State University. His project at Clemson has been to study the biochemistry of the two enzymes in terms of their growth and metabolism. Dang will be fully supported by the NIH grant as a graduate research associate.
"Entamoeba is a really fascinating organism in that it lacks many essential metabolic pathways commonly seen in other organisms," Dang said. "However, it has found ways to adapt, some of which might be novel to the world. Our work hopes to elucidate further on this neglected parasite and its mysteries."
* Cheryl Jones, who was born and raised in Anderson, graduated this past May with her Ph.D. in biochemistry and molecular biology. Jones received her bachelor's degree in biochemistry in 2009 from Clemson. She was a recipient of the prestigious National Science Foundation Graduate Research Fellowship as well as a Wade Stackhouse Fellowship. While still at Clemson, she studied how one of the enzymes functions biochemically. Jones has one publication from this work and another that will be submitted this summer. She is currently a postdoctoral research associate in the University of North Carolina at Chapel Hill's cellular biology and physiology department.
"Working on this project has awoken a passion in me for exploring the fascinating biology of parasites," Jones said. "Yet, it also opened my eyes to the millions of people suffering from devastating diseases like amoebic dysentery. Global health is a global responsibility, and I've been fortunate to make my contributions here at Clemson."
Ingram-Smith said her research is unlikely to lead directly to a cure, but what her team uncovers will add to a database of knowledge that will increase the chances of developing a vaccine or medication that could eventually rid the world of one of its most widespread and aggressive pathogens.
"The goal of this research is to determine what roles these two enzymes play and understand how that fits in with the overall growth of Entamoeba," Ingram-Smith said. "A better understanding of how Entamoeba survive under different conditions should prove helpful in discovering ways to combat this disease. It's always better to be proactive than reactive."