X-ray analysis uncovers how malaria drugs work

Editorial

Rebecca Pool

Friday, November 1, 2019 - 11:00
Image: The vacuole of a malaria parasite (blue and green) inside an infected blood cell. [Kapishnikov]
 
Researchers have shed new light on malaria pathogens in red blood cells in vivo using the Germany-based BESSY II X-ray microscope and the ALBA and ESRF synchrotron sources in Spain and France.
 
Analyses reveal the mechanisms used by active substances to attack the pathogen, paving the way to better treatment strategies and drugs.
 
Malaria pathogens are unicellular organisms, known as plasmodia, that settle inside the red blood cells of hosts and metabolize haemoglobin, to grow and multiply.
 
Quinolene is widely used to combat malaria, but exactly how its active compounds keep plasmodia in check remains controversial.
 
When plasmodia digest haemoglobin, heme is liberated as a by-product, which is toxic to the parasites.
 
However, past research suggests that this heme can be rendered inert by crystallization into hemozoin, within the plasmodia digestive vacuole. 
 
The combination of these methods revealed how the presence of bromoquine hinders the detoxification process of the plasmodia. [Kapishnikov]
 
With this in mind, Sergey Kapishnikov from the University of Copenhagen and the Weizmann Institute of Science in Rehovot, Israel, and colleagues, set out to see if the active compounds within the anti-malarial drug, quinolene, block crystal formation to boycott heme detoxification. 
 
They first infected blood cells with the malaria pathogen Plasmodium falciparum, and then mixed samples with different concentrations of bromoquine from the quinoline family.
 
They went on to examine samples using X-ray microscopy at BESSY II and the ALBA synchrotron light source in Barcelona.
 
“The blood samples are flash-frozen for the examination so that we can observe the pathogens in vivo and also produce three-dimensional X-ray tomography images,” explains Kapishnikov's colleague, Peter Guttmann.
 
The researchers also used fluorescence spectromicroscopy at the European Synchrotron Radiation Facility in Grenoble to map elemental distribution in the blood cells.
 
By combining these results with the cellular structure revealed by the 3D X-ray images, they could precisely observe bromoquine distribution and its mode of action.
 
“We see in our images that the bromoquine accumulates at the surface of hemozoin crystals,” says Kapishnikov. “This should lead to inhibition of the crystal growth and thus disrupt the detoxification process by the plasmodia parasites.”
 
The researchers now intent to extend their investigations to other anti-malarial drug groups such as Artemisinin and provide valuable information for the design of more effective treatments. 
 
Research is published in PNAS.
 
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