A newly discovered compound could lead to breakthrough treatments for various diseases.

Researchers from Rice University have synthesized a new generation of contrast agents for tagging and real-time tracking of stem cells in the body by combining ultrashort carbon nanotubes and bismuth clusters that show up on X-rays taken with CT scanners.

According to the researchers, the stable compound performed more than eight times better than the first-generation material introduced in 2013.

Rice chemist Lon Wilson said the compound—called Bi4C@US-tubes—will help treat diseases.

“The primary application will be to track them in stem-cell therapies to see if the cells are attracted to the site of disease—for example, cancer—and in what concentration,” Wilson said in a statement. “Magnetic resonance imaging is currently used for that purpose and it works quite well but X-ray technology in the clinic is much more available.

“It’s faster and cheaper and it could facilitate preclinical studies to track stem cells in vivo.”

Bismuth is commonly used in cosmetics, pigments and pharmaceuticals, notably as the active ingredient in the antacid Pepto-Bismol.

For the study, the scientists developed bismuth nanoclusters and combined them with carbon nanotubes chemically treated to shorten them to between 20 and 80 nanometers and add defects to their side walls.

The nanoclusters, which make up approximately 20 percent of the compound, appear to strongly attach to the nanotubes via the defects.

According to Wilson, the treated nanotubes are easy to spot when they are introduced into stem cells.

“It’s very interesting to see a cell culture that is opaque to X-rays,” Wilson said. “They’re not as dark as bone (which X-rays cannot penetrate) but they’re really dark when they’re loaded with these agents.”

The research team tested the compound in a CT scanner at St. Luke’s Baylor Hospital, which compared the abilities of empty nanotubes, the previous generation of Bi@US-tubes and the new compound with Hounsfield units used to measure X-ray attenuation of contrast agents.

The experiment resulted in about 188 Hounsfield units being identified for plain ultrashort nanotubes, 227 for older Bi@US-tubes and 2,178 for the latest compound.

The majority of soft tissue fall between 30 and 100 Hounsfield units, so cells labeled with the new compound were expected to stand out.

After further testing the clusters showed to hold tight to their nanotubes and no bismuth was released from the nanotubes tested at body temperature over 48 hours.

According to Wilson, the next step will be for the Food and Drug Administration to approve the new compound for use in humans.

“But we’re in a position to start preclinical studies now that we’ve determined how well we can load cells and the fact that cells are not seemingly harmed by the technology and short bursts of X-rays,” Wilson said.    

The study was published in ACS Applied Materials & Interfaces