Scientist - News - 19-02-2009:

Probiotics-induced changes in the intestine
Beintema, Nienke

Probiotics activate certain genes in the intestinal wall, according to a recent study by Wageningen University. Most of these genes are involved in the immune response of healthy adults. The results represent the first molecular evidence of the effect of probiotics. Lead researcher Michiel Kleerebezem: "The pattern was very clear."

It was no news that probiotics can influence certain immune parameters. How that influence is effectuated at the molecular level, however, was still unknown. A study by the Top Institute Food and Nutrition (TIFN) now shows that living cells of Lactobacillus plantarum activate certain genes in the intestinal wall. These genes play an important role in the immune response of healthy adults. The results appeared in PNAS Online (February 4th).
This new information is important, according to lead researcher Michiel Kleerebezem. "The effect of probiotics is based on a combination of very complex mechanisms," he explains. "In fact we know very little about this. Probiotic products, for instance, are usually tested on the basis of trial and error: what works, and what doesn’t? But that is not very efficient when it comes to the follow-up questions: which probiotics are most effective, in which quantities, and with which production method?"

Cooled
The Wageningen study showed, for instance, that the growth stage of the bacteria has an impact on their effect. The researchers tested fast-growing L. plantarum cells, as well as mature cells and even dead cells. "Each of the three categories triggered another pattern of cellular reactions," says Kleerebezem. "The reaction of the mucosal tissue of the intestine is apparently related to the way in which the probiotic is administered. The mature bacterial cells have the most pronounced immune-regulating effect. In that respect there is a nice match with the products that are currently on the market: these contain bacteria that indeed stopped growing."
In other aspects, however, there may be room for improvements by producers. For instance, the food product in which the probiotics are administered makes a difference. "Many of the current products are cooled dairy products," says Kleerebezem, "but if the bacteria are contained for instance in fruit juice, it is uncertain whether the clinical claims still hold in these products. Relevant studies are lacking: scientists usually look into the characteristics of different probiotics in the lab. In this respect our research shows that it is justified to critically examine the method of administering probiotics."

Similar patterns
The Wageningen researchers studied eight healthy individuals, who came to the lab four times at two-week intervals. During these consecutive visits, the volunteers consumed four different drinks in a random order: a placebo, and sports drinks with dead, growing or mature L. plantarum cells. For each volunteer, the researchers studied the differences between the four treatments. They also compared the treatment between individuals. To do that, they took biopsies from the small intestine. These tiny fragments of the intestinal wall were tested for their gene expression patterns.
"Remarkably enough," says Kleerebezem, "there were major similarities between the subjects in terms of the reactions in their mucosal tissue after consumption of the probiotic drinks, even though the individuals differed strongly with regard to their diet and habits."
In all volunteers, living, mature L. plantarum cells activated roughly the same group of three to seven hundred genes. Most of these genes are known to play a role in the immune response. "The next challenge is to identify the underlying biological meaning of these lists of genes," Kleerebezem remarks. "We have software and statistical packages for that, based on established gene functions. But it also requires some detective work into the role of individual genes."

‘Code orange’
The researchers have been able to reconstruct part of the biology of the intestine’s mucosal tissue. "The pattern was very clear," states Kleerebezem. "These genes aren’t random, but part of a group of related genes that correspond with entire molecular pathways." These are exactly the so-called NF-κB-dependent pathways that play an important role in the regulation of the immune response of healthy adults. According to the interpretation of the researchers, L. plantarum induces a higher level of alertness in the immune system. "The immune system is set to ‘code orange’, so to speak," says Kleerebezem, "which allows it to react adequately when the need arises."
This phenomenon has never been shown in a lab before. As a next step, the group would like to check whether this increased alertness really translates into a stronger immune reaction in response to an immune challenge, for instance a mucosal vaccin. In addition, the researchers are planning to study the effect of other probiotics.

The precise molecular mechanisms continue to intrigue Kleerebezem and his colleagues. One of the remaining questions is how the bacteria manage to activate the genes of the intestinal wall. Do they excrete certain chemicals, for instance, that induce these patterns? "That is in fact crucial information," states Kleerebezem. "We would like to elucidate that communication mechanism in order to influence it, or even improve it. But it could also be useful as a means of quality control: to check whether a product contains not only the probiotic, but also the molecules that induce the desirable effect. So far, quality controls have only been based on counts of living cells in the product, so a molecular marker for functionality would be ideal. In any case our research is a valuable step in that direction."

More information:
Press release on website TIFN
Publication in PNAS