Have you heard about the gut microbiome—the very, very large collection of good and bad bacteria, viruses, fungi, and other microorganisms that lives within all of us? When there is a healthy balance of good and bad microorganisms, the body functions well. But when the gut microbiome gets out of balance, the immune system can go awry.
The gut microbiome is a hotbed of research these days—and one of the key areas that is being looked at for its links to immune diseases such as multiple sclerosis (MS), inflammatory bowel disease, type 1 diabetes, and rheumatoid arthritis.
The Human Microbiome Project
There are trillions of microorganisms that reside in the human body. In fact, microorganisms outnumber human cells by 10 to 1. Using recently developed DNA technology to analyze tissue samples collected from the mouth, nose, skin, and vaginas of 242 healthy men and women, the Human Microbiome Project, a $157 million, five-year research study launched in 2007 by the National Institutes of Health, has mapped all of the microorganisms that normally live in or on the human body.
This and other research revealed that there are many beneficial bacteria in the human microbiome that help our bodies perform essential functions, but there are also potentially dangerous bacteria, known as pathogens. Everyone carries these pathogens, but in healthy people they don’t cause disease.
This finding has since spurred much new research, including some looking specifically at MS and the gut microbiome, says Ilana Katz Sand, M.D., associate professor of neurology at Icahn School of Medicine at Mount Sinai in New York City.
What have MS studies found about the gut microbiome?
The largest study to date was recently published in the journal PNAS and was conducted by the MS Microbiome Consortium, a group of researchers from four centers located in California and New York City. “We analyzed the gut bacteria profile of 71 people with MS compared with 71 healthy control subjects and found that there were a couple of different groups of bacteria that were more common in people with MS, and there were some that were less abundant in people with MS than in healthy people,” reports Dr. Katz Sand, one of the study investigators.
Specifically, people with MS had increased bacterial counts of Akkermansia muciniphila and Acinetobacter calcoaceticus, which are known to induce more inflammatory activity in the body, and a lower level of Parabacteroides distasonis, which is known to induce more anti-inflammatory activity. A Harvard study published in 2016 found similar changes in the bacterial profiles of people with and without MS, as well as an abundance of more protective bacteria in people with MS who were on the disease-modifying therapy glatiramer acetate (Copaxone).
“We know that there is definitely an association between the gut microbiome and MS, but most studies have been relatively small, so we have to validate the results in a larger group of patients,” says Dr. Katz Sand. “We also know that MS is caused by some combination of genetic risk and environmental risk. In terms of environmental risk, we know about smoking, viruses, and vitamin D a little bit, but a whole chunk of environmental exposures is still missing,” she says.
The gut is a natural place to look next, she adds, because about 70 percent of the body’s immune system is housed inside the gut, and MS is known to be a disease characterized by an overactive immune system. The immune cells that live in the gut communicate with the rest of the body, including the brain.
The bacteria also secrete different products that have effects on the body and these products can make their way into the bloodstream and the central nervous system. For instance, it’s possible that the MS gut microbiome profile may lead to a heightened autoimmune response and the stripping of the protective padding around nerve fibers (demyelination) in the central nervous system, which is the hallmark of MS.
In addition to finding out about the bacterial profile that is unique to the disease, researchers also need to tease out the cause-and-effect relationship between the gut microbiome and MS. “Is it that these changes in the microbiota are present first and lead to increased susceptibility to MS?” she asks. “Or is it that as people develop the disease, the microbiota changes? We really don’t know, and it will take us a while to figure out what it all means. We also don’t have a clear idea of how MS medications may affect the gut microbiota or how an individual’s profile may affect their response to treatments.”
Moving toward new therapies
The great hope of studying the link between MS and the gut microbiome, of course, is that it will lead to new treatments. Dr. Katz Sand and her colleagues are in the process of conducting a small trial with 36 subjects looking at a dietary intervention to change the bacterial composition of the gut and reduce inflammation in people with MS.
“We have put people on a fairly restrictive, modified Mediterranean-type diet that largely consists of fruits, vegetables, and healthy fats from fish, avocados, and nuts,” she says. “They can’t eat meat, dairy products, or processed foods.” The group plans to complete the study in the spring of 2018 and publish results thereafter.
Other approaches might be to alter the bacterial composition of the gut microbiome by supplementing patients with probiotic supplements that contain lactobacilli or other health-promoting bacteria, or performing a fecal transplant, whereby fecal matter from a healthy donor is transplanted into a person with MS to rebalance the gut microbiome.
“Research into the gut microbiome and MS is still in the early stages, but what we’re seeing is exciting,” concludes Dr. Katz Sand.
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