Durk Pearson & Sandy Shaw’s®
Life Extension NewsTM
Volume 14 No. 3 • June-July 2011


Gut Microbiota (Resident Microbial Community in the GI Tract) Affect Host Use of Selenium

The gut microbiota is currently a very hot research subject because the community of gastrointestinal resident microbes is being found to have many important effects on immune activity, growth, and use of ingested nutrients, as well as metabolism of important food components such as flavonoids, inflammation, and many other aspects of health. For example, in obese mice and humans it has been found that, in comparison to their lean counterparts, obesity tended to be associated with an enhanced proportion of Firmicutes, reduced Bacterioidetes, or both.1 In a new paper,2 it is reported that dietary selenium affects the host’s production and metabolism of selenium-containing proteins by influencing the gut microbiota. The results showed that the intake of selenium by the host influenced the composition of the intestinal microflora and the microflora, which, in turn, importantly affected the host’s use of the available selenium. In this study,2 10 week-old germ-free (these animals had no gut microbiota) Swiss Webster mice were supplemented with selenium at different doses (0, 0.1, and 0.4 ppm selenium). One group was maintained germ free, while the other two groups were “conventionalized” by receiving microflora from the intestine of C57BL/6J mice.

Perhaps the most interesting finding was that selenium in the diet increased the diversity of the microbiota. The authors also found that “within the 0.1 ppm selenium groups, we observed higher Gpx1 [glutathione peroxidase 1] expression in the liver and kidney, and higher Gpx [glutathione peroxidase] in kidneys of GF [germ-free] mice, compared to CV [conventionalized] mice.” The latter finding relates to the fact that the microbes sequester some of the ingested selenium for their own use.

The authors did identify some specific changes in the makeup of the microbiota as a result of different levels of selenium supplementation, though these changes cannot be clearly interpreted in terms of an “obese vs. lean” microbiota, as not enough is known about these changes to make such correlations. By far the most significant effect on the microbiota, relative to absolute abundance in this study was the decline in Parabacteroides (a subgroup of bacteroides) in response to selenium in the diet.

Incidentally, the authors chose the 0.1 ppm selenium to mimic the human recommended dietary allowance for adults, whereas 0.4 ppm selenium may (the authors suggest) correspond to the diet supplemented with 200g selenium/day in human clinical trials involving selenium.

Consistent with the triage theory discussed above, the authors found that some selenoproteins, such as Gpx1 and MsrB1 (methionine-R-sulfoxide reductase 1) are sensitive to selenium status whereas several other selenoproteins, including TR1 (thioredoxin 1) were less susceptible to selenium changes. “Thus, mice and other mammals have a priority for Se [selenium] supply that is selenoprotein and tissue specific.”

References

  1. Turnbaugh and Gordon. The core gut microbiome, energy balance and obesity. J Physiol 587:4153-8 (2009).
  2. Kasaikina et al. Dietary selenium affects host selenoproteome expression by influencing the gut microbiota. FASEB J 25:2492-9 (2011).

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