Trillions of microbes can be found in the human body, with most living in the gastrointestinal tract. These microbial communities, or microbiomes can have a profound impact on human health and well-being, by modifying molecules in the foods we eat or generating their own proteins that can effect the human body, for example. Researchers are starting to identify specific links between certain microbes, the molecules they alter or create, and human health or disease. Scientists have now shown that intestinal bacteria help control blood vessel aging. The findings have been reported in Nature Aging.
Cardiovascular disease causes the most deaths worldwide, and as we age, we are at higher risk of cardiovascular problems. As the inner lining of blood vessels, or endothelium ages, cardiovascular disease can arise.
This research analyzed health data from over 7,000 healthy people between the ages of 18 and 95, as well as a mouse model of aging. This analysis showed that a byproduct of the breakdown of the amino acid phenylalanine known as phenylacetic acid builds up during aging.
The investigators then showed that phenylacetic acid caused endothelial cells in blood vessels to stop dividing, a state known as cellular senescence. Since the blood vessel lining stops rejuvenating at that point, inflammatory molecules are secreted and aging starts. The blood vessels then begin to stiffen and harden, which impairs their function and can lead to cardiovascular disease.
The study also determined that a bacterium called Clostridium sp.ASF356, which is present in the gut microbiomes of mice and people, can convert phenylalanine into phenylacetic acid.
When the investigators exposed young mice to these bacteria, the mice started to carry high levels of phenylacetic acid levels and showed symptoms of vascular aging. Antibiotics were then used to eliminate the bacteria from the mice. After that, the levels of phenylacetic acid in the mice dropped.
"We were thus able to show that the intestinal bacteria are responsible for the increased levels," said first study author Soheil Saeedi of the University of Zurich.
While this situation may cause problems for people, there are also many benefits that come from the gut microbiome. Short-chain fatty acids, for example, are known to be produced by gut bacteria, and they have a beneficial impact on human health.
This study also confirmed that; when the short chain fatty acid (SCFA) acetate was added to aged endothelial cells, some function was restored. The research indicated that in aging, the levels of these beneficial SCFAs also goes down.
"The aging process of the cardiovascular system can therefore be regulated via the microbiome," suggested Saeedi.
The scientists want to learn more about how diet can be used to aid human health through the microbiome. For example, certain foods that contain high levels of phenylalanine, like dairy products, red meat, and some artificial sweeteners could be limited in an effort to stave off vascular aging. It may also be possible to use medications to reduce the levels of phenylacetic acid, though more research is needed to confirm that these methods can benefit vascular health.
Sources: University of Zurich, Nature Aging