Gut bacteria sensitive to salt, linked to MS and hypertension: study

20 Nov 2017 --- Common salt reduces the number of certain lactic acid bacteria in the gut of mice and humans. This is according to a study published in the journal Nature by Berlin's Max Delbrück Center and Charité, which further notes an impact on immune cells that are partly responsible for autoimmune diseases like multiple sclerosis (MS) and hypertension. Probiotics were also found to ameliorate the symptoms of disease in mice.

We eat salt every day, and we often eat too much, notes the study. “But so far, nobody had studied how salt affects the bacteria in the gut,” says head of the study Professor Dominik Müller of the Berlin Experimental and Clinical Research Center (ECRC) and the Berlin Institute of Health (BIH), both of which are joint institutions within the Max Delbrück Center for Molecular Medicine and the Charité – Universitätsmedizin Berlin.

Lactobacilli work on salt’s harmful effects
Too much salt in food can encourage hypertension and might even have a negative impact on the course of autoimmune diseases like MS. Now Müller and his team have demonstrated that excess salt decimates the lactobacilli in the gut while blood pressure rises and the number of Th17 helper cells is increased. These immune cells are associated with hypertension and autoimmune diseases like MS.

When the animals were given probiotic lactobacilli in addition to the high-salt diet, however, the frequency of Th17 helper cells decreased once again and blood pressure dropped. The probiotics also alleviated the clinical symptoms of experimental autoimmune encephalomyelitis, a disease model for MS.

The researchers thus identified the microbiome as an important factor in diseases affected by salt. “Gut bacteria influence the host organism, and the immune system is also very active in the gut,” says lead author and ECRC scientist Dr. Nicola Wilck.

Müller and Wilck worked together with an interdisciplinary research team including Professor Ralf Linker from FAU Nürnberg-Erlangen, scientists from Massachusetts Institute of Technology (MIT) in Boston, US, from the European Molecular Biology Laboratory (EMBL), Heidelberg, the University of Regensburg and the Vlaams Instituut voor Biotechnologie (VIB) in Hasselt, Belgium. The German Centre for Cardiovascular Research (DZHK) also supported the study.

Pilot study with human test subjects
Apart from the experiments on mice, the researchers also investigated the bacterial community in the digestive tract of 12 healthy men who were given six extra grams of salt every day for two weeks.

As the test subjects otherwise maintained their usual eating habits, they thus roughly doubled their daily intake of salt. Here, too, the lactobacilli responded sensitively. Most of them were no longer detectable after 14 days of increased salt intake. At the same time, scientists discovered that the subjects’ blood pressure rose and the number of Th17 helper cells in the blood increased.

Discoveries could be used for therapy
More and more research is focusing on the role played by bacteria in very different types of diseases. Exactly how the organism interacts with gut flora is still largely unknown, however.

“Our study goes beyond just describing the changes caused by salt. We want to consider interrelated processes,” says Müller. But so far, they have not managed to completely explain the precise interactions; he admits: “We can't exclude the possibility that there are other salt-sensitive bacteria that are just as important.”

Moreover, the study’s new findings have not actually confirmed the therapeutic effect of lactobacilli, which are found in fermented food such as sauerkraut, yogurt and cheese.

“Multiple sclerosis may be one of the salt-sensitive diseases which we might be able to treat in the future with individually-tailored probiotics as add-on to standard immune therapies,” notes neuroimmunologist Professor Ralf Linker. Lactobacillus probiotics of this kind have therapeutic potential.

This will soon all be examined at ECRC, says Wilck: “We are planning a blood pressure study with human subjects: double-blind with a larger number of participants of both genders and placebo-controlled.” After that, the team can start thinking about the therapeutic application of probiotics.