By :- Team VOH
28 Jun 2024
Researchers from the Department of Bioengineering (BE) at the Indian Institute of Science (IISc) have created a novel 3D hydrogel culture system that simulates the mammalian lung environment. This system provides an advanced platform to study how tuberculosis (TB) bacteria infect lung cells and to test the efficacy of TB treatments, according to a press release from the Bengaluru-based IISc.
Mycobacterium tuberculosis (Mtb), a dangerous pathogen, infected 10.6 million people and caused 1.3 million deaths in 2022, according to the WHO.
"Mtb is a very old bug, and it has evolved with us quite a bit," says Rachit Agarwal, Associate Professor at BE and corresponding author of the study published in "Advanced Healthcare Materials." Mtb primarily infects the lungs.
Current culture models used to study Mtb infection have several limitations. These models typically use monolayered culture plates that do not accurately replicate the 3D microenvironment inside the lungs. The microenvironment in 2D cultures is vastly different from the actual extracellular matrix (ECM) surrounding lung tissue, IISc explains.
"In a tissue culture plate, there are no ECM molecules, and even if a very thin layer of ECM is coated on these plates, the lung cells 'see' the ECM on one side at best," explains Vishal Gupta, a PhD student at BE and the first author of the study. The 2D culture plates are also much harder compared to the soft lung tissues. "You are looking at a rock versus a pillow," adds Agarwal.
Agarwal and his team designed a novel 3D hydrogel culture made of collagen, a key molecule present in the ECM of lung cells. Collagen is soluble in water at a slightly acidic pH, and as the pH increases, the collagen forms fibrils that cross-link to create a gel-like 3D structure.
During the gelling process, the researchers added human macrophages—immune cells involved in fighting infection—along with Mtb. This trapped both the macrophages and the bacteria in the collagen, allowing the researchers to track how the bacteria infect the macrophages. The team observed the infection progression over 2-3 weeks. Remarkably, the mammalian cells remained viable for three weeks in the hydrogel, whereas current cultures sustain them for only 4-7 days, the release said.
"This makes it more attractive because Mtb is a very slow-growing pathogen inside the body," says Agarwal.
The researchers performed RNA sequencing of the lung cells grown in the hydrogel and found that they were more similar to actual human samples compared to those in traditional culture systems.
The team also tested the effect of pyrazinamide, one of the four most common drugs given to TB patients. They found that even a small amount (10 g/ml) of the drug was quite effective in clearing out Mtb in the hydrogel culture. Previously, scientists had to use large doses of the drug—much higher than concentrations achieved in patients—to show its effectiveness in tissue culture. "Nobody has shown that this drug works in clinically relevant doses in any culture systems. Our setup reinforces the fact that the 3D hydrogel mimics the infection better," Agarwal explains.
Agarwal adds that they have already filed an Indian patent for their 3D culture, which can be scaled up by industries for drug testing and discovery. "The idea was to keep it quite simple so that other researchers can replicate this," he adds.
Moving forward, the researchers plan to mimic granulomas—clusters of infected white blood cells—in their 3D hydrogel culture to explore why some people have latent TB while others show aggressive symptoms. Gupta says the team is also interested in understanding the mechanism of action of pyrazinamide, which may help discover new drugs that are more efficient.
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