Researchers have transferred bacteria from the guts of long-lived people to those of mice, and the results have some interesting implications for healthy aging and show why maintaining a good microbial balance in the gut is one of the keys of staying healthy as we age.
The gut microbiome
The gut microbiome is comprised of a varied community of bacteria, archaea, eukarya, and viruses. The four bacterial phyla of Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria comprise 98% of the intestinal microbiome.
The microbiome community is a complex ecosystem whose activity regulates a number of functions in the gut and interacts with the immune system and energy metabolism. The beneficial bacteria in our guts also help to prevent the growth of harmful bacteria, protect us from invasive microorganisms, and help to maintain the integrity of the intestinal barrier.
There is evidence that the balance of the gut microbiome is critical in maintaining health during aging, with some studies suggesting that a poor gut microbiome contributes to atherosclerosis, immune system decline, breast cancer, sarcopenia, and many other diseases. The microbiome is also a proposed origin point for the age-related chronic inflammation known as “inflammaging“, which is common in older people and likely facilitates various diseases.
The rise and fall
As we age, the balance and populations of the gut microbiome typically change, with the amounts of beneficial bacteria generally falling and the harmful ones increasing. The gut microbiomes of long-lived people tend to have much better diversity and balance than those typically seen in older people, with some studies suggesting that their microbiomes are similar to those of much younger people.
A new study published in the journal Aging further supports the idea that a healthy microbiome is a significant determinant of longevity and health, and its results show that the microbiome can also be transferred between species.
The researchers here took the unusual approach of using fecal transplants taken from long-lived people and giving them to mice. The mice were then examined to see if there were positive changes to the populations of beneficial bacteria living in their guts. It turns out that the mice given these fecal transplants had a greater gut microbiome diversity, and their intestinal structure was improved for better nutrient absorption. The aging biomarkers lipofuscin and ß-galactosidase were also present in lower concentrations than their untreated littermates.
The researchers reported that the presence of Lactobacillus increased in the treated mice. This particular probiotic species is generally considered friendly and can be found in fermented foods, yogurt, and supplements. Long-lived people tend to have a higher population of this species.
The mice also had elevated populations of Bifidobacterium, another probiotic bacteria associated with long-lived individuals. Bifidobacterium scavenges reactive oxygen species, activates the stress-response gene, regulates the activity of nuclear factor ?B, and inhibits the production of pro-inflammatory cytokines from macrophages.
Roseburia ferments prebiotics, plant products that contain dietary fiber, into butyrate, which is used by gut microbes and colonocytes as energy. Butyrate is also a histone deacetylase inhibitor; induces generation of colonic regulatory T cells; induces antimicrobial peptide production of colonocytes; prevents expansion of pathogenic commensals; and inhibits toll-like receptor 4 signaling. The SCFA butyrate is estimated to be responsible for approximately 70% of the energy created by colonocytes, making it the most important SCFA in colon homeostasis.
Faecalibacterium influences metabolism and immune cell activity and is one of the most abundant and important commensal bacteria in the human gut microbiota. With age, the population of faecalibacterium typically declines, and this decline is associated with Crohn’s disease and other intestinal disorders.
Ruminococcus is a bacteria found in the gut microbiome that appears to play a role in breaking down plant cell walls, thus helping us to ferment and digest plant-based foods. The fermentation of digestion-resistant starch is thought to contribute significantly to the production of butyrate in the colon and is conducted by Ruminococcus bromii in particular.
Coprococcus bacteria actively ferment carbohydrates, producing butyric and acetic acids with formic or propionic and/or lactic acids. There is some evidence they may protect against colon cancer in humans by producing butyric acid, and low levels of this bacteria may be linked to depression.
A close relationship between age and gut microbiota exists in invertebrates and vertebrates, including humans. Long-living people are a model for studying healthy aging; they also have a distinctive microbiota structure. The relationship between the microbiota of long-living people and aging phenotype remains largely unknown. Herein, the feces of long-living people were transplanted into mice, which were then examined for aging-related indices and beneficial bacteria. Mice transplanted with fecal matter from long-living people (L group) had greater a diversity, more probiotic genera (Lactobacillus and Bifidobacterium), and short-chain fatty acid producing genera (Roseburia, Faecalibacterium, Ruminococcus, Coprococcus) than the control group. L group mice also accumulated less lipofuscin and ß-galactosidase and had longer intestinal villi. This study indicates the effects that the gut microbiota from long-living people have on healthy aging.
The importance of the gut microbiome and its populations of bacteria is becoming increasingly apparent in the goal of understanding aging and intervening against it in order to preserve health. Effective ways to transfer beneficial bacteria to populate the gut is a low-hanging fruit that could help us to remain healthier as we grow older.