Tiny tools tackle malaria

Optical tweezers stretch a healthy red blood cell (top) and a cell in a late stage of infection with the P. falciparum malaria parasite (bottom) Copyright: Suresh et al.

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Researchers at the Massachusetts Institute of Technology, United States, have shown how tiny tools can help address big problems — in this case, understanding malaria.

Subra Suresh, head of the institute’s department of materials science and engineering, has led a study using ‘optical tweezers’ to show how the elasticity of red blood cells changes when they are infected with the malaria parasite.

The flexibility of these cells determines how they and the parasites within them move through the body. Understanding this is important to understanding the disease.

Optical tweezers are an example of a nanotechnology tool. After fixing miniscule beads of the mineral silica to opposite sides of a red blood cell, then focusing a laser beam on each one, researchers can move the beads and stretch the cells by moving the lasers.

Healthy red blood cells are disc-shaped, with a slight depression on either side. Their flexibility allows them to squeeze through the smallest blood vessels, before reverting to their original shape.

Infected blood cells, on the other hand, are more rigid and the researchers were unable to stretch cells in the later stages of infection.

Suresh’s results confirm findings that were made by Dutch researcher Arjen Dondorp in 2000, but using optical tweezers has allowed him to define the difference in elasticity with greater precision.

In fact, the research shows that red blood cells in the late stage of infection, known as the schizont stage, are ten times stiffer than healthy red blood cells.

Suresh explains that not much is known about the later stages of infection, when cells become ‘sticky’. This means conventional methods, which involve sucking the cells into the narrow neck of a pipette to see how easily they can squeeze into small spaces, are imprecise.

Suresh’s team is now comparing the way different species of the malaria parasite affect the elasticity of red bloods cells.

Plasmodium falciparum, the most widespread malaria parasite, is responsible for the most deaths worldwide. Plasmodium vivax, in contrast, is much less widespread and not as deadly.

Researchers speculate that this may in part be due to the different mechanics of infected cells, and that cells infected by P. vivax are much more flexible than those infected by P. falciparum.

This could mean that the former continue to circulate in the bloodstream, and are eventually destroyed in the spleen, whereas those infected with P. falciparum get stuck in small blood vessels of other organs, such as the brain.

“One advantage of optical tweezers is they provide greater flexibility to test the mechanics [of infected cells] more accurately,” says Suresh. For instance, researchers can attach several silica beads to a red blood cell and explore the detail of how it responds to pulling in different directions.

There has been much speculation about the harm that could come from nanotechnologies —products created at a scale of one-tenth the width of a human hair. Because of small size of nanotechnology products and because the field is relatively new, many fear nanotechnology will develop faster than corresponding regulations, leading to potential health and environmental risks.

The Canadian ETC Group has been particularly vocal on this topic, calling for a moratorium on “nanotechnology products that touch the human body” including pesticides, cosmetics, and water purification systems.

But Pat Mooney, executive director of ETC, agrees that many applications of nanotechnology may prove very useful and advantageous to the world’s poor.

“We expect to find thousands of examples where nanotechnology can be very useful,” says Mooney, specifying that he is more concerned about the social understanding and control of the technology.

Brian Greenwood, professor of clinical and tropical medicine at the London School of Hygiene and Tropical Medicine, United Kingdom, told SciDev.Net that the optical tweezers were “a very elegant technology to address an important question”.

Suresh and his colleagues published their results in this month’s issue of the journal Acta Biomaterialia.

Link to full paper by Suresh et al in Acta Biomaterialia and video clips of cells being stretched

Reference: Acta Biomaterialia 1, 15 (2005)

COMING SOON: Read more about nanotechnology in SciDev.Net’s new quick guide to nanotechnology, which will be launched early in February 2005.