The bacterium that causes ulcers and some stomach cancers, Helicobacter pylori, could at least contribute to Parkinson's disease, according to a new study in mice presented at a microbiology conference yesterday. Mice infected with H. pylori have shown Parkinson's-like symptoms, building on earlier work that has suggested a link between the bacteria and Parkonson's disease. How the Heck:
What's the News:
The researchers infected mice with H. pylori. Middle-aged mice (who'd been around for the equivalent of 55 to 65 human years) began to move in abnormal ways, a hallmark symptom of Parkinson's disease, and had decreased levels of the neurotransmitter dopamine in certain parts of the brain. This suggests that the murine subjects' dopamine-producing neurons may have been dying off, as they do in human patients with Parkinson's disease. Young mice were unaffected, paralleling how people are more susceptible to Parkinson's as they age.
Next, the researchers fed killed, ground-up H. pylori to another group of mice, instead of infecting them with living bacteria. Again, the mice in midlife showed Parkinson's-like symptoms, meaning it could be a biochemical component of the bacteria, rather than the whole organism, that triggers the disease.
These results "suggest that H. pylori infection could play a significant role in development of Parkinson’s disease in humans," the researchers wrote.
What's the Context:
Scientists have long suspected a link between H. pylori and Parkinson's disease. Earlier studies have shown that Parkinson's patients are more likely than average to be infected with H. pylori and to have developed ulcers during their life.
Internist Barry Marshall pinpointed H. pylori as the cause of ulcers in the early 1980's---and proved it by drinking some of the bacteria himself then taking a biopsy from his own gut when he began to develop an ulcer.
In Guam, people have developed a dementia much like Parkinson's after eating cycad seeds. H. pylori makes a modified cholesterol molecule that is structurally similar to a toxic compound in the cycad plant, suggesting a possible mechanism by which the bacteria could trigger the disease.
Not So Fast:
This was a preliminary study in mice, meaning much more research needs to be done before researchers can definitively say the H. pylori contributes to Parkinson's disease in humans.
The study also had some methodological limitations. Mice in the study were infected with relatively high levels of the bacterium compared to what you might find in people, and the researchers didn't directly measure whether dopamine-making cells were in fact dying as a result of the infection.
Reference: Traci Testerman. "Bacteria may cause Parkinson’s disease." Presented at the 111th General Meeting of the American Society for Microbiology, May 22, 2011. Image: Helicobacter pylori, National Cancer Institute