Carnegie Mellon University researchers have discovered that an element commonly found in nature might provide a way to neutralize the potentially lethal effects of a compound known as Shiga toxin. New results published in the Jan. 20 issue of Science by Carnegie Mellon biologists Adam Linstedt and Somshuvra Mukhopadhyay show that manganese completely protects against Shiga toxicosis in animal models.
Produced by certain bacteria, including Shigella and some strains of E. coli, Shiga toxin can cause symptoms ranging from mild intestinal disease to kidney failure. The findings could pave the way for future research aimed at creating an inexpensive treatment for infections caused by bacteria that produce the lethal Shiga toxin. Currently there is no treatment for such infections that afflict more than 150 million people each year, resulting in more than one million deaths worldwide.
Such infections are common in developing countries where it causes waterborne epidemics. It can be particularly deadly, especially in children, as it causes dysentery and severe hemorrhagic diarrhea, which cannot be adequately treated in areas without access to clean water. In developed countries, Shiga toxicosis is most common during foodborne outbreaks — like the widespread E. coli outbreak this past summer in Germany and Western Europe, where more than 3,700 people were infected and 45 died.
After entering the body, Shiga toxin is secreted by the infecting bacteria. It then attaches itself to a surface receptor on a cell's plasma membrane and enters the cell through a process called endocytosis. Normally, when a harmful substance enters a cell in this way, it's wrapped in a package called an endosome and sent directly to the cell's lysosome where it is degraded and discarded.
"That's exactly the process that Shiga toxin avoids. It would be neutralized if it were to get degraded, so it had to find some way to get out of being sent to the lysosome," said Linstedt, professor of biological sciences at Carnegie Mellon.
Linstedt and Mukhopadhyay discovered exactly how Shiga toxin avoided the lysosome as they were doing basic biological research to understand how components of the cell function. "If we weren't focused on answering fundamental biological questions, we wouldn't have made this discovery," Linstedt said.
Fifteen years ago Linstedt discovered GPP130, a protein found in the Golgi apparatus, a kind of post office for the cell that sorts and packages molecules made in the endoplasmic reticulum and delivers them to their final destinations within the cell. GPP130, Linstedt found, didn't behave like most Golgi proteins. Rather than remaining in the Golgi, GPP130 constantly cycles to the endosomes and back to the Golgi. As it returns, it avoids the pathway that takes a substance to the lysosome to be degraded.
"I knew that Shiga toxin was one of the key cargo molecules that bypass the lysosome as they go from the endosome to the Golgi apparatus, so I figured it would be a good marker to study in relation to GPP130. What I didn't realize was how profoundly dependent Shiga toxin was on GPP130," Linstedt said.
But the most serendipitous aspect of this discovery can be traced to a phone call made four years ago. Don Smith, a toxicologist at the University of California, Santa Cruz, who was studying manganese toxicity, noticed that GPP130 was sensitive to manganese. He called Linstedt who began to do a series of experiments on how manganese affects GPP130. Around this time Mukhopadhyay joined Linstedt's lab for his post-doctoral training. He quickly discovered that as concentrations of manganese rise inside the cell, GPP130 changes its pathway and goes directly to the lysosome where it is degraded.
Because Shiga toxin was dependent on GPP130 and manganese caused loss of GPP130, Linstedt and Mukhopadhyay decided to see whether manganese would protect against Shiga toxin infection. In cell cultures, manganese treatment yielded an almost 4,000-fold increase in the amount of Shiga toxin required to induce cell death. In a mouse model, mice exposed to a high dose of Shiga toxin and treated with non-toxic doses of manganese were 100 percent resistant to the toxin.
By introducing manganese, Linstedt and Mukhopadhyay were able to remove Shiga toxin's vehicle for avoiding degradation — GPP130. The researchers feel that this could be a promising treatment for neutralizing the effects of Shiga toxin in humans.
"Manganese is inexpensive. While Shiga toxin infection affects people in the developed world, it affects far more people in the developing world. An inexpensive, accessible treatment — not a designer drug — is the ideal solution," Linstedt said. "We know the toxicity levels of manganese in humans; we know ways to administer it. While further testing is needed to determine if manganese is a suitable treatment for humans, I'm optimistic that trials should move forward quickly."
The researchers also believe that manganese might be able to be used in conjunction with antibiotics. Currently, if an infected person is given an antibiotic, the antibiotic kills the bacteria (E. coli or Shigella) that produce the toxin. This releases the toxin in larger amounts and causes a higher percentage of patients to die. Linstedt believes that they can use manganese to block the toxin and an antibiotic to kill the bacteria, making for an extremely effective therapy.
The Carnegie Mellon researchers plan to continue their research by using situations that more closely mimic Shiga toxin infection in humans, and by testing their antibiotic/manganese combination therapy in mouse models. The researchers also will pay attention to manganese toxicity. High doses of manganese can have severe neurotoxic effects. The amounts used in the current study were low enough that they didn't cause any side effects in the mouse models.
Carnegie Mellon University: http://www.cmu.edu
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
After a severe brain injury, some people remain in a vegetative or minimally conscious state, unable to speak or move intentionally, and apparently unaware of the world around them. But in recent years, neuroscientists have found signs that some of these patients may still be conscious, at least to a degree. Now researchers have used a branch of mathematics called graph theory to search for neural signatures of consciousness.
Few parasitoids are more bizarre or disturbing than the wasps of the genus Glyptapanteles, whose females inject their eggs into living caterpillars. Once inside, the larvae mature, feeding on the caterpillar’s body fluids before gnawing through its skin en masse and emerging into the light of day. And despite the trauma, not only does the caterpillar survive---initially at least---but the larvae proceed to mind-control it, turning their host into a bodyguard that protects them as they spin their cocoons and finish maturing. Then, finally, the caterpillar starves to death, but only after the tiny wasps emerge from their cocoons and fly away.
From their new book A History of Life in 100 Fossils, Paul Taylor and Aaron O'Dea share the story of 10 incredible fossils
We love origin stories. When we see successful groups of animals and plants, we wonder where they came …
First research of its kind shows that tasers could impair a person's memory and thought process
Sometimes the most fascinating animals are the ones that are no longer with us. The oddly named sthenurine is no exception.
Australian banded stilts use mysterious cues to know when to head toward ephemeral lakes in the country’s otherwise dry interior
The intriguing story of how whale evolution was unpicked is told in The Walking Whales, revealing what it's like to be a globe-trotting palaeontologist
Cells derived from embryos appear to have improved vision in more than half of the 18 patients who had become legally blind because of two progressive, currently incurable eye diseases.
Oil rigs are rarely lauded by conservationists, but fish seem to love them – they have more fish living around them than natural rocky reefs do