Is there a relationship between gut microbiota and circulating metabolites?

The role of the gut microbiota has been demonstrated in many disorders (obesity, diabetes, etc.): metabolites and other microbial signals could affect the amount of circulating lipids, including triglycerides and HDL. Several studies have also established a link between gut microbiota and several amino acids implicated in diabetes and cardiovascular diseases. Building on progress in the field of metabolomics, a team has evaluated the relationship between gut microbiota and circulating metabolites. This was done via characterization of the metabolome (all metabolites) from 2,309 individuals from 2 prospective cohort studies (Rotterdam and LifeLines-DEEP). It emerged from this that a total of 32 bacterial groups were associated with certain circulating metabolites after adjusting for age, sex, body mass index (BMI) and medication (including lipid-lowering agents, proton pump inhibitors and metformin).

Microbiota and lipoproteins

Among the 32 microbial taxa identified, 18 were associated with VLDL particles (associated in turn with metabolic and cardiac diseases, and type 2 diabetes), and 22 others with HDL particles (well known for their protective role), with, however, differences depending on the size of the HDL particles, suggesting that this class of lipoproteins is heterogeneous with respect to its metabolic functions and effects (protective or harmful). 13 microbial taxa–of which some are well known for their association with BMI (Christensenellaceae), others for their association with bile acid metabolism (Clostridiaceae 1), etc.–were associated with both VLDL and HDL particles. However, the unclear association between gut microbiota and LDL and IDL (sidenote: Intermediate Density Lipoprotein ) * particles suggests there are different relationships depending on the class of lipoproteins. Finally, 15 bacterial groups, including the Ruminococcus gnavus group (sign of a less diverse gut microbiota and more present in patients with atherosclerosis), were associated with serum triglycerides.

Ketone bodies, amino acids, etc.

Associations were also reported between gut microbiota and:

• ketone bodies, notably acetates of short-chain fatty acids (SCFAs) produced by colonic bacteria which could promote metabolic syndrome.

• amino acids including isoleucine, associated with diabetes mellitus and cardiovascular diseases.

• acute phase inflammatory markers, notably glycoproteins implicated in inflammatory diseases and cancer, and associated with cardiovascular diseases.

According to the authors, the potential mechanisms by which gut microbiota could affect the amount of circulating lipids could implicate bile acids and SCFAs. If so, the gut microbiota could become a potential target for curative and preventive interventions.