Urine test for tuberculosis
Nanoparticles will help diagnose tuberculosis by urine analysis
Daria Spasskaya, N+1
Thanks to a new sensitive method of detecting a polysaccharide marker of the causative agent of tuberculosis, the disease can now be diagnosed by urine analysis. The main component of the technique was a new polysaccharide-binding chemical complex. Scientists sewed it to nanoparticles that can be incubated with urine and then extracted from there, concentrating the polysaccharide in this way. As the authors of the technology published in Science Translational Medicine have shown, the method allows not only to detect the presence of an active form of tuberculosis in patients, but also to determine the severity of the disease, and is suitable for conducting tests in the field.
According to WHO, tuberculosis affects several million people in the world every year (more than 10 million in 2015 and more than 6 million in 2016), and more than a million die from this disease every year. 80 percent of cases occur in 22 countries, which include Russia. The key to successful treatment is timely diagnosis of tuberculosis. Currently, the main tools for detecting the disease in adults are radiography, microbiological studies and identification of the DNA of the pathogen – bacteria Mycobacterium tuberculosis. However, these methods require special equipment, are sometimes not too accurate and take a long time.
Scientists are working on new testing tools that are fast, accurate and cheap enough to be used in the field. A promising approach is the diagnosis of urine analysis. Until now, tuberculosis could be suspected in this way only in patients with kidney damage. However, scientists were able to detect pulmonary tuberculosis by the presence in the urine of a component of the mycobacterium cell wall – lipoarabinomannan (LAM). So far, the sensitivity of the test was only enough to diagnose the disease in patients with human immunodeficiency virus (this group accounts for 15 percent of the total number of patients). Such patients, due to suppressed immunity, are characterized by a high load of the pathogen, so the concentration of LLAMAS in their urine is high enough to detect it using enzyme immunoassay.
Researchers from George Mason University in Virginia (USA), led by Alessandra Luchini, managed to increase the sensitivity of the technique to a level sufficient to detect tuberculosis in ordinary patients. To do this, scientists "fished" LLAMAS out of urine using hydrogel nanoparticles with a polysaccharide binding complex sewn to them.
A new LAM-specific chemical complex based on copper (Reactive Blue 221) binds a polysaccharide with a strength 100 times greater than known proteins specific to it. The complexes were "sewn" onto the edges of cellular nanostructures made of hydrogel. Iron oxide particles were also attached to the nanoparticles so that they could be conveniently concentrated using a magnet. The suspension of particles was incubated with a milliliter of urine, then nanoparticles were concentrated and the presence of LAMAS was determined using antibodies.
A. Nanoparticles with chemical complexes sewn to them (red) that capture tuberculosis antigen (yellow), in this case LAM. B. Schematic diagram of the analysis. Nanoparticles are incubated with urine and then concentrated. c. Structure of LAM and its binding complex RB221 (Luisa Paris et al / Science Translational Medicine 2017).
The researchers were able to confirm the diagnosis in 48 patients of the hospital in Lima (Peru), who have not yet started receiving treatment. As a control, the analysis was performed on 39 healthy volunteers and another 14 patients with other diseases, for example, lung cancer, pneumonia or urogenital infections. In people not suffering from tuberculosis, LAM was not detected in the urine. The accuracy of tuberculosis detection exceeded 80 percent, and the sensitivity of the test was more than 95 percent.
The researchers also found that LAM can be quantified, and an increase in its concentration in urine correlates with other signs of the disease, such as weight loss and cough. Thus, with the help of the technique, it is possible to determine the severity of the disease.
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