ILP Institute InsiderFebruary 6, 2013
Probing the Malarial Shape Shifters
Developing nano tools to study the parasites at the root of one of the world's greatest health threats.
Last November, GlaxoSmithKline reported a disappointing 30 percent effectiveness in a trial for its RTS,S anti-malarial vaccine. RTS,S had been championed as the most promising vaccine for the mosquito-borne disease, which infects 300 to 500 million people a year while killing nearly one million, according to CDC estimates. The news followed reports that malaria is becoming increasingly resistant to existing treatments like Artemisinin.
The world health community is now scrambling to identify new anti-malarial solutions. The need is growing more urgent, says Ming Dao, Principal Investigator for malarial research at MIT's SMART Infectious Disease Interdisciplinary Research Group (ID-IRG).
"Malarial infections are one of the top human health threats, second in infections only to HIV/AIDS," says Dao, who is also Principal Research Scientist at the Nanomechanics Laboratory in MIT's Materials Science & Engineering Department. "Mosquito nets have helped bring down the infection rate, but malarial parasites have become very clever in adapting to new treatments and drugs."
The fact that a materials science laboratory is leading a major medical research project shows just how closely the worlds of nano- and biotechnology have aligned. It turns out that many of the measurement tools and techniques used to develop and test nano-engineered materials can also be used to explore the inner workings of biological cells.
Dao and his colleagues are adapting sophisticated nanoscale measurement tools developed at the Nanomechanics Lab in conjunction with new biomechanical models to explore the behavior of host red blood cells infected by the deadliest of the malarial parasites, Plasmodium falciparum. The findings are helping to establish novel diagnostic devices as well as to identify new drugs and treatment targets that could eventually disrupt malaria-infection-induced changes in red blood cell deformability, stickiness, and shape. Altering these traits could potentially limit both the effects of malaria and the chances for infection.
Dao began applying nanoscale biomechanical research to malaria in 2004 under the direction of MIT Dean of Engineering Subra Suresh. When Suresh became Director of the National Science Foundation in 2010, Dao was assigned to oversee the Nanomechanics Lab (Suresh Lab) while Suresh took a leave of absence from MIT. With intellectual input and guidance from Suresh, Dao and his colleagues have continued the research in collaboration with genetics and infectious disease experts at MIT and around the world.
"Malaria is a fascinating disease," says Dao. After the Plasmodium parasites (sporozoites) are injected, typically via a mosquito bite, they quickly infect the liver cells, he explains. "They hide there for a week or two, then multiply asexually and come out into the blood stream as merozoites and infect red blood cells," says Dao. Within 24 hours, these multiplied parasites invade new host red blood cells and asexually reproduce more merozoites within 48 hours.
Researchers at the Nanomechanics Laboratory confirmed earlier studies that found that during this 48 hour asexual cycle, the parasites "modify the human host red blood cell, making it much stiffer and stickier," Dao explains. "These infected cells tend to sequester, sticking to each other and to blood vessel walls, and cause painful symptoms and even fatalities."
The researchers also found that the RESA protein is responsible for stiffening the host cells during the first 24 hours. In addition, they demonstrated how RESA strengthens the membrane during this period to protect against the fevers caused by malaria. During the second 24-hour period, RESA steps aside, and other proteins take over, making the cells stickier, thereby encouraging sequestration.
If one of these early stage, asexual merozoites is drawn by a mosquito, it cannot reproduce or be retransmitted, says Dao. "Only the small number of late-stage gametocytes transformed to the sexual form can infect a new human host through a mosquito vector," he adds.
Dao and his colleagues set out to solve several mysteries posed by the malaria cycle. Why was it, for example, that the sexually matured "stage 5" gametocytes were the only ones to be found floating freely in the bloodstream? If the early-stage gametocytes sequestered in order to avoid being filtered out by the spleen, then why didn't the late-stage mature gametocytes do the same?
Working with the Harvard School of Public Health, the team used a transgenic line for 3D live imaging to study the infected cells with various nanoscale measuring tools, in vitro capillary assays, and 3D finite element cell modeling. The researchers found that at stage 5, the gametocytes return to a much more compliant state. This increased deformability, combined with changes in shape, "enables them to go through the small opening in the spleen and get into microcirculation," says Dao.
This research enables a novel way of seeking anti-malarial solutions, says Dao. "We may be able to find gene or drug disruptions of mature sexual parasites to make them much stiffer so they cannot pass the spleen clearance," he says. "We could aim to disrupt the biomechanical properties and keep them from circulating and retransmitting."
Bio Research Refines Nano Tools
Dao's malaria research would not have been possible without the latest nanoscale measurement equipment, including optical tweezers, nano-indentation probes, atomic force microscopes, and light scattering phase microscopy. "We use very precise probes to create very small forces that poke into cells to measure stiffness," says Dao.
In some cases, the Nanomechanics Laboratory has developed new tools specially designed for biomechanical study. In the process, they have advanced the field of nanomechanics measurements in general.
"We have worked on a new generation of optical tweezers that can test red blood cell mechanics, and we have modified atomic force microscopes to better measure stiffness and adhesion," says Dao. Collaborating with the George R. Harrison Spectroscopy Laboratory, the researchers have experimented with a new generation of light scattering phase microscopy and tomography to measure cell membrane fluctuations. "You can even measure the 3D shape and volume of the parasite and hemoglobin," adds Dao.
One tool that was particularly helpful in understanding whether the infected cells can pass through the capillaries and spleen is microfluidic technology. "With these new onboard microfluidic chips you can now effectively and quickly make a diagnostic platform," says Dao.
Nano Tools Applied to Head Trauma, Sickle Cell
The new tools being refined at the Nanomechanics Lab are also being applied to a separate malaria project with the Singapore-MIT Alliance for Research and Technology (SMART) Center to develop a humanized mouse model for malarial infection. "This involves biomechanics because human red blood cells are larger than those (red blood cells) in a mouse," says Dao. "We're also trying to understand if there's a way to block the parasite invasion of the red cell."
The team has also applied these tools and techniques in studying head trauma caused by shock waves from bomb blasts or sports injuries. "We can now go down to the cellular level, and see how neuron cells behave under high speed impacts," says Dao. "Our studies help us to understand why these neuron cells are damaged and what areas are more vulnerable."
Additional projects include a collaboration with Brown University on a Dissipative Particle Dynamics (DPD) model for molecular and cellular mechanics studies. DPD "lets you study molecular processes in blood cells and malarial infected cells at a realistic timescale and length scale," says Dao. In addition, Dao and his team recently began applying their nanoscale tools to the problem of sickle cell disease.
Meanwhile, Dao continues to play a key role in nanomaterials research. For example, to solve the problem of the loss of ductility and durability in metals created with sub 100-nanometer grain sizes, the team has collaborated with researchers in China to develop a more resilient nanoscale twin microstructure.
Dao attributes the lab’s continued success to the guidance and leadership of Dr. Suresh, as well as the contributions from Nanomechanics Lab students and researchers, especially Monica Diez Silva. Yet, the collaborations have extended across MIT and the world. "In just about any research area you choose at MIT, chances are you are going to find top-notch researchers to work with," says Dao. "MIT is also a strong magnet for attracting collaborations around Boston and the world."
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