Lipids produced by gut bacteria contribute to atherosclerosis
According to the World Health Organization, ischaemic heart disease and stroke were responsible for a combined 15 million deaths in 2015, making them the commonest killers worldwide. Heart disease and stroke have been linked to atherosclerosis, a slow, progressive condition in which arteries become clogged with lipid deposits, or called plaques. Immune response to these lipids drives the formation of the plaque by triggering a chronic inflammatory reaction.
Eating food high in fat, lipid, or cholesterol can increase a person's risk of developing atherosclerosis. Examples of this kind of food are cheese, eggs, shellfish, and organ meats. However, not all people who often eat these foods develop atherosclerosis. What makes the difference remains unknown.
A team composed of researchers from the University of Connecticut School of Medicine, Texas Tech University Health Sciences Center, Harvard School of Dental Medicine, the University of California Los Angeles, and Hartford Healthcare Medical Group conducted a study to better elucidate the cause of atherosclerosis.
Findings of the study, which were published in the Journal of Lipid Research on 16 August 2017, suggest that it may be the lipids produced by bacteria in the mouth and intestine that drive the development of atherosclerosis. This would improve early disease diagnosis, according to a co-senior author of the study, Dr. Xudong Yao from the University of Connecticut.
The team made this discovery by analyzing the chemical characteristics of lipids in artery samples from patients. With the help of mass spectrometry (MS) and other techniques, the team found that in these samples, there was a class of lipids that were not from animals but from a group of bacteria, known as Bacteroidetes.
Bacteroidetes bacteria are commonly found in the human mouth and intestine. Some Bacteroidetes bacteria help break down food and produce valuable nutrients for the body. But the bacteria sometimes can cause or exacerbate infections.
Bacteroidetes bacteria produce so much serine dipeptide lipids. The researchers called them 'greasy bugs'. The study revealed chemical and weight differences between Bacteroidetes lipids and human lipids, which could explain why Bacteroidetes lipids trigger atherosclerosis. Additionally, the study also suggested that Bacteroidetes lipids might be degraded by enzymes like phospholipase A2 (PLA2)
in the body to produce proinflammatory factors. PLA2 enzymes are widely present in mammalian tissues and play key roles in inflammatory responses.
In summary, the study indicates that Bacteroidetes bacteria in the mouth and intestine may contribute to the development of atherosclerosis by producing large amounts of serine dipeptide lipids. Although more research is needed to elucidate the precise mechanisms, the study would have implications for the intervention of atherosclerosis, heart disease as well as stroke.