Probiotics communicate with the people who consume them. The nature of this communication is the subject of much research. This research can tell us a lot about how probiotics do what they do (this can be important to regulatory authorities and customers), and can help us predict what types of clinical trials might be successful (this can help wise investments in probiotic efficacy research).
The nature of this communication between probiotic lactobacilli and healthy adults is the subject of a randomized, double-blind, placebo-controlled cross-over study by several Dutch scientists (Baarlen et al. 2011). They measured how human intestinal tissue (proximal small intestinal or duodenal mucosa to be exact) responded when healthy adults consumed 3 probiotic strains, L. acidophilus Lafti-L10, L. casei CRL-431 and L. rhamnosus GG. Probiotic strains and a placebo were administered individually to all subjects, with a 2-week wash out period between administrations of each strain. The response the scientists measured was the types of RNA that were produced (transcriptomes) by the people consuming them, 6 hours after probiotic consumption. The set of RNAs produced reflects the host genes that are expressed in response to exposure to the probiotics. Observations included the following:
- Each probiotic strain induced differential genes in the human mucosa.
- Variation between persons was larger than variation between strains. This may help explain responders and non-responders in human probiotic intervention trials.
- Differential expression of several hundred up to thousands of genes was observed, including genes involved in immune function, the cell cycle, blood pressure, and water and ion homeostasis.
- Normally colonized human mucosa mounted fast and specific responses to the probiotic lactobacilli.
The authors noted that responsiveness to probiotics is not only determined by characteristics of the specific probiotic strain, but likely also involves genetic background, resident microbiota, diet, and lifestyle of the consumer. This is an important observation in the context of understanding how small changes in processing or matrix might affect efficacy of a probiotic. This suggests that differences in host genetics and diet may be more important than, for example, if the probiotic is delivered in milk compared to yogurt.
Another important observation made by the authors has to do with conceptualizing an appropriate niche for probiotics in the framework of consumer health. They state: “Research into probiotics might use a similar approach as nutrigenomics research that is based on the idea that nutrition should focus primarily on health and disease prevention and be complementary to medical therapy that is used to prevent or cure more progressed disease.”
van Baarlen P, Troost F, van der Meer C, Hooiveld G, Boekschoten M, Brummer RJ, Kleerebezem M. Human mucosal in vivo transcriptome responses to three lactobacilli indicate how probiotics may modulate human cellular pathways. Proc Natl Acad Sci U S A. 2011 Mar 15;108 Suppl 1:4562-9.