Image: A diagram depicting high internal/external surface area ratio and binding capacity of nanocages. Affinity ligands covalently immobilized in the inner volume establish high-affinity noncovalent interaction with tuberculosis (TB) antigens (Photo courtesy of George Mason University).
An accurate screening test for active pulmonary tuberculosis (TB) is urgently needed for patients who are not co-infected with human immunodeficiency virus (HIV). Worldwide, TB is one of the most prevalent bacterial infections, with the highest mortality in developing countries.
Ideally, such a test would use a noninvasive body fluid such as urine to facilitate utilization in a low-resource setting. This objective, at first, appears straightforward because the outer surface glycan lipoarabinomannan (LAM), a TB antigen shed into the urine during active TB, has been identified and well characterized.
An international team of scientists collaborating with those at George Mason University (Manassas, VA, USA) applied a copper complex dye called RB221 within a hydrogel nanocage that captures LAM with very high affinity, displacing interfering urine proteins. The technology was applied to study pretreatment urine from 48 Peruvian patients, all negative for HIV, with microbiologically confirmed active pulmonary TB by auramine staining for acid-fast bacilli in sputum and microscopic-observation drug-susceptibility (MODS) assay. Patient urine samples were qualified before the analysis by urinary dipstick testing.
The scientists found that the RB221 nanocages trapped LAM from urine, increasing detection sensitivity by 100- to 1,000-fold, all while excluding interfering compounds from the samples that could confound results. In 48 Peruvian HIV-negative tuberculosis patients who had not yet been treated, the new test detected infections with greater than 95% sensitivity and a specificity of greater than 80%. LAM was quantitatively measured in the urine in a concentration range of 14 to 2,000 pg/mL, as compared to non-TB, healthy and diseased, age-matched controls.
Elevated LAM concentrations in urine correlated with increased amounts of bacteria and more severe disease (as measured by weight loss or cough). The team also created nanocages to trap and detect other hallmarks of infection including very low abundance molecules named the 6 kDa early secretory antigenic target (ESAT6) and the 10-kDa culture filtrate protein (CFP10). Sandwich and lateral flow immunoassay feasibility for testing clinical specimens was documented for ESAT6. According to the authors, their next steps are to compare urinary LAM in patients before and after therapy to evaluate potential treatment-induced changes. The study was published on December 13, 2017, in the journal Science Translational Medicine.
George Mason University