Possible new method identified for assessing severity of TB infection – Washington University School of Medicine in St. Louis
Researchers at Washington University School of Medicine in St. Louis have discovered a molecule in the lungs of tuberculosis (TB) patients that mirrors the levels of tuberculosis-causing bacteria in the lungs, information needed to better treat the notoriously hard-to-treat disease.
The findings, published Feb. 1 in the Journal of Clinical Investigation, could be a step toward better treatment regimens and better outcomes for TB patients.
Most of the 10 million people who develop TB each year undergo months of treatment with multiple antibiotics, and despite the expensive drug regimen, about 5% of TB patients relapse within two years. Doctors don’t have a good way to track bacteria levels in their lungs, so they watch for symptoms instead.
But the new research identifies a molecule in people with active TB and shows that levels of this molecule are higher in people with more severe infections. The molecule is a derivative of cholesterol known as cholestenone.
“It’s hard to guide clinical care and make treatment decisions when you don’t have a good way to measure if you’re actually reducing the amount of bacteria,” the lead author said. Jennifer A. Philips, MD, Ph.D., Associate Professor of Medicine and Molecular Microbiology. “A reduced cough, lowered fever, weight gain and general feeling of strength are all good signs that what you are doing is working, but they are not proof that the bacteria have been eliminated. Some of the medications that we use are very toxic and we have to use multiple drugs for a long time We probably overtreat a whole bunch of people but we can’t tell the people who might stop taking them sooner from the people who need to go more long, otherwise they will relapse.
Like all living beings, Mycobacterium tuberculosis, the bacteria responsible for tuberculosis, must eat. It consumes chemical compounds and releases by-products as it breaks down the compounds into energy, a process known as metabolism. Philips and his colleagues – including co-first authors Pallavi Chandra, a medical instructor with a PhD in microbiology, and Héloise Coullon, a researcher with a PhD in pharmacy and microbiology – felt they might be able to identify infected cells and individuals by detecting the presence of by-products of bacterial metabolism.
To search for such compounds, the researchers infected mouse cells with tuberculosis bacteria and then used mass spectrometry to identify the metabolic compounds released over the next five days. Some cells were left uninfected for comparison. The researchers discovered more than 30 compounds that distinguished infected cells from uninfected cells. One of the most striking differences was in levels of cholestenone, a byproduct of bacterial cholesterol metabolism. Tuberculosis bacteria can metabolize cholesterol, but they do not make it themselves. they acquire it from people during infection. People also metabolize cholesterol, but by a different process that does not generate cholestenone. Thus, cholestenone is a unique cometabolite produced by bacteria during infection, making it a promising candidate for identifying people with active tuberculosis and measuring the amount of bacteria in their lungs.
The researchers studied 80 people, half in Vietnam and the other half in Peru, where tuberculosis is more common than in the United States. All of the participants had symptoms of lung infection such as fever, cough and weight loss, but only half had tuberculosis. The remaining 40 people – 20 from each country – had other reasons for their symptoms, such as other types of lung infections.
With the help of Xuntian Jiang, PhDAssistant Professor of Medicine and Director of University of Washington Metabolomics Facility, the researchers analyzed sputum samples, produced deep in the lungs, of the 80 participants. Tuberculosis patients had significantly higher cholestenone levels in their sputum than people without tuberculosis. And among TB patients, those who had more TB bacteria in their lungs had higher levels of cholestenone.
Sputum is not ideal for monitoring levels of TB bacteria in the lungs because acquiring it for analysis requires the patient to cough intensely to bring it up from deep within the lungs and then spit it out. Some people, especially children, just can’t handle it. But blood tests are an integral part of medical care. If TB patients have high levels of cholestenone in the blood, as is the case in sputum, it might be possible to create a blood-based way to measure levels of TB bacteria and monitor the effectiveness of treatment. .
Philips and his colleagues tested cholestenone levels in blood samples from the 80 participants. Among people in Peru, researchers were able to distinguish those with and without TB by their blood cholesterol levels. Among those in Vietnam, however, the levels were not different between the two groups.
“It’s really exciting to find a difference in the levels in patients in Peru,” Philips said. “We are really interested in understanding what is different between the two populations because then we might be able to find a different metabolite of cholesterol to measure which is a blood biomarker of bacterial levels in all TB patients. There could be many reasons why it worked in Peru but not in Vietnam. This may be due to differences between people in Vietnam and Peru in terms of genetics or bacteria in their microbiomes. Tuberculosis bacteria themselves belong to different lineages in Peru and Vietnam, which may also be a factor. We are continuing this project and exploring as many of these possibilities as possible.