Small, harmless doses of the metallic element manganese may completely defend cells against the effects of Shiga toxin, the deadly poison produced by harmful strains of E. coli and Shigella that can induce severe diarrhea, intestinal complications and hemolytic uremic syndrome (HUS) in infected individuals. That is according to a study published in Science on January 20 by two Carnegie Mellon University researchers.
In laboratory tests, the researchers found that mice were 100 percent resistant to Shiga toxin exposure after receiving a small, non-toxic injection of manganese. In fact, a cell culture model showed that manganese treatment made animal cells 4,000 times more resistant to Shiga toxin.
If further testing proves successful, the discovery could lead to an inexpensive, highly effective treatment for E. coli and Shigella infections, said Adam Linstedt, Ph.D., molecular biology professor at Carnegie Mellon and lead author of the study. Right now, there is no available treatment for Shiga toxin poisoning.
“There’s a very reasonable chance that this could be effective in saving lives,” Linstedt told Food Safety News.
The discovery, described as “serendipitous” by Linstedt and co-author Somshuvra Mukhopadhyay, came about during some basic research of cell protein function. They were studying a unique protein called GPP130, which cycles between a cell’s Golgi apparatus and its endosomes, unlike similar proteins that simply remain in the Golgi apparatus.
The researchers knew that GPP130 was somehow involved in trafficking Shiga toxin through cells. They eventually found that when Shiga toxin invades cells, it binds to GPP130 to avoid being broken down by a cell’s lysosome. The protein then carries the toxin back to the Golgi apparatus, endoplasmic reticulum and eventually the cytoplasm, where it begins attacking protein synthesis and kills the cell.
Four years ago, through a phone call from a colleague at the University of California Santa Cruz, Linstedt learned that exposure to manganese causes GPP130 to change pathways, traveling to the lysosome to be degraded. Linstedt soon realized that if Shiga toxin relies on GPP130 and manganese removes GPP130 from cells, manganese could be used as a treatment to block Shiga toxin.
“The moment we thought of that, it seemed too good to be true,” Linstedt said. “It seemed that it would work, but if you do any research like this at all, you know 9 times out of 10 these things don’t work out. This seems to be one of those rare occasions when it actually does.”
Lindstedt said that they have not yet found any side effects from the degradation of GPP130. He has a theory that the protein plays a role in manganese homeostasis, the function regulating manganese levels in the body.
Now, the question of timing comes into play: People infected with Shiga toxin-producing bacteria — like E. coli O157:H7 — typically don’t know they’re infected until they start exhibiting injurious symptoms that eventually lead to vascular damage.
But Linstedt believes there is a reasonable window of time in which to treat patients between the onset of bloody diarrhea and the eventual vascular damage, which begins developing approximately four days later. In the cell culture study, GPP130 took three to six hours to completely degrade, meaning that the cells became resistant to the toxin in that amount of time.
“If you have a four-day window to treat people, that leaves plenty of time for the manganese treatment to take effect,” Lindstedt said.
Linstedt’s proposed treatment would combine manganese with antibiotics for a one-two punch against E. coli. Traditionally, antibiotics are not used to treat E. coli infections because the bacteria’s death produces an influx of toxin release. But if cells are completely immune to the toxin, medical staff should be free to kill off the bacteria without fear of causing more harm than good.
Vetting that theory will involve another round of testing. Linstedt and Mukhopadhyay plan to test-run the manganese-antibiotic combination on mice infected with Shiga toxin-producing E. coli. Linstedt said that using E. coli bacteria instead of a purified form of the toxin should provide a better understanding of how the treatment would work in a real-world setting.
Another step will involve pinpointing the minimum manganese dose required to inoculate GPP130. To prove their concept in the initial mouse study, the researchers administered a dose of manganese that was still too small to be toxic, but far larger than necessary.
Linstedt credits this discovery to the more basic, gritty side of science: Searching for fundamental knowledge that unlocks unforeseen insights that could one day save lives.
“It was in doing the basic research that we were led to this discovery,” Linstedt said. “It’s not the sort of thing you’d come across without first trying to answer very basic questions about cells.”