Probiotics: When good bacteria turn bad
In brief, probiotics are living microorganisms that people are now consuming as a way of influencing their gut bacteria.
The concept of people improving their intestinal health by eating live organisms is not a new one but dates back almost 100 years.
Today, however, the idea is mainstream. Grocery stores across the United States sell a range of products that contain probiotics and offer the promise of improved gut health.
Despite their growing popularity and impressive claims, research into the potential health benefits of probiotics is still relatively sparse and not entirely positive.
For instance, a recent study — which researchers did not design specifically to test the efficacy of probiotics — has uncovered some rather negative news about them.
University of Texas engineers carried out the study at the Cockrell School of Engineering in Austin, using cutting-edge, organ-on-a-chip technology.
This type of investigation allows scientists to attach human cells to microchips and, depending on the cell type they chose, watch them mimic any organ in the body.
Specifically, the scientists were interested in understanding why inflammation arose in the digestive system.
They recently published their work in the Proceedings of the National Academy of Sciences, in a study that marks the first time that an organ-on-a-chip has modeled the development of a disease.
To date, scientists have found it challenging to understand exactly why and how gut inflammation develops.
The process involves communication between the epithelial cells that line the gut, the immune system, and the microbiome.
These physiological components engage in a chemical dialogue that involves a dizzying array of secretions — and deciphering the interactions is difficult.
The current investigation wanted to understand whether the organ-on-a-chip approach might help yield some answers. Study lead Hyun Jung Kim explains why designing such a model is important:
“By making it possible to customize specific conditions in the gut, we could establish the original catalyst, or onset initiator, for the disease,” Kim says, adding, “If we can determine the root cause, we can more accurately determine the most appropriate treatment.”
The researchers concluded that the main driver of gut inflammation is the health of the intestinal epithelium — specifically, its permeability.
The intestinal epithelium is a thin layer of cells that have a protective role — namely, to prevent toxins and bacteria from the gut leaching out into the rest of the body, where they could cause harm.
How do probiotics fit in?
As part of their study, the scientists considered the impact of probiotics. They found that so-called good bacteria might be healthful for some people but have a negative health impact for others. It seems that their influence depends on the integrity of the intestinal epithelium.
“Once the gut barrier has been damaged, probiotics can be harmful just like any other bacteria that escape into the human body through a damaged intestinal barrier.”
Researcher Woojung Shin
Shin, a biomedical engineer who worked with Kim on the project, continues, “When the gut barrier is healthy, probiotics are beneficial. When it is compromised, however, they can cause more harm than good. Essentially, ‘good fences make good neighbors.'”
Dysfunction of the epithelial membrane — sometimes referred to as a leaky gut — appears to play a role in a wide range of health conditions, including inflammatory bowel disease, irritable bowel syndrome, obesity, food allergies, and celiac disease.
Because it is so prevalent, understanding whether probiotics might be unhealthful for people with these conditions is critical.
In the future, Shin and colleagues plan to extend their findings and develop more customized intestinal disease models. Shin is interested in gathering more insight into how gut bacteria impact inflammation, how cancer spreads, and the performance of anticancer drugs.
Although more work will be needed to firm up these conclusions, they call into question the current one-size-fits-all approach to probiotics. Because of their newfound popularity, understanding how they might impact individuals with compromised intestinal epithelia is vital.
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