B. adolescentis positively linked with blood glucose level, say scientists

The study was conducted by a group of researchers from Genome Institute of Singapore, Singapore Immunology Network, National University of Singapore, and Vrije Universiteit Amsterdam.

Pre-print version of the study findings were published pre-print on bioRxiv. ​

The study looked at the gut microbiome of 234 Singaporean elderly between the age of 71 and 100.

Deep shotgun metagenomic was used to analyse their gut microbiomes.

The results were also compared to reference shotgun metagenomic data from healthy, younger Singaporeans who were from two other age groups, namely between 53 and 74 years old and between 21 and 80 years old.

The study identified over 10 robust gut microbial associations to inflammation, cardiometabolic and liver health.

Of which, the study found two associated species, namely Bifidobacterium adolescentis ​and Parabacteroides goldsteinii​, ​to be positively linked to fasting blood glucose, confirming findings from previously in vitro ​and in vivo ​studies.

It also found that Lactobacillus mucosae ​was positively linked with fasting blood glucose – a finding which has never been described before, the researchers said. 

These are however, purely associations derived from the data, and do not mean that there is a clear cause and effect relationship, the authors stressed.

Aside from blood glucose, the study also found positively association between total cholesterol levels and Lachnospiraceae bacterium​ 1 4 56FAA.

Total cholesterol levels, however, was negatively associated with Haemophilus parainfluenzae, ​meaning the lower the amount of Haemophilus parainfluenzae, ​the higher the total cholesterol levels.

This is again, another finding which has never been reported previously.

Notably, an opposite trend was seen for low-density lipoprotein (LDL)-cholesterol or the “bad cholesterol”.

In this case, the higher the amount of Haemophilus parainfluenzae, ​the higher the LDL-cholesterol levels, while the lower the amount of Lachnospiraceae ​species, the lower the LDL-cholesterol levels.

“These observations indicate potential beneficial roles of Lachnospiraceae species in maintaining lower levels of LDL. ​

“Interestingly, microbial association with triglyceride levels was dominated again by positive association with Haemophilus parainfluenzae, a species that has been described to be strongly enriched in patients with chronic cholecystitis patients and individuals with increased risk of cardiovascular disease.” ​

In addition, the abundance of Klebsiella pneumoniae ​is found to be associated with high serum levels of the enzyme aspartate aminotransferase (AST). High serum levels of AST is a sign of liver damage.

The authors added that Klebsiella pneumoniae ​was a sporadic coloniser of the gut microbiome, and a known pathogen for liver abscesses that are increasingly common in Asian populations.

Shift in microbiome in elderly ​

The study also found a shift in gut microbiome amongst the elderly, such as a reduction in microbial richness. 

In particular, it reported a depletion in the ‘microbial guild’ of butyrate producing bacteria species.

This depletion was replaced with the increase in specific Alistipes species that can produce butyrate through an alternate pathway using amino acids as precursors.

In particular, there was an increase in Alistipes shahii, ​as well as Bacteroides xylanisolvens. ​

“The gut microbiomes of healthy octogenarians exhibited a defined shift in diversity and overall taxonomic composition, as a function of age and independent of other covariates.”​

“We also noted an enrichment with age for multiple Alistipes species, including Alistipes shahii, Alistipes onderdonkii and Alistipes senegalensis, that are bile tolerant, have a unique way of fermenting amino acids such as L-lysine, and can produce neurotransmitter precursors such as indole.​

“In contrast, several species that are known to be important for butyrate production in the gut, including Faecalibacterium prausnitzii, Roseburia inulinivorans and Eubacterium hallii, were significantly depleted with age,”​ said the researchers.

Butyrate is of interest as it has diverse roles in host health, including reducing gut inflammation.

“In particular, we provide the first well-powered species-level view of microbiome shifts as a function of age, with a steady decrease in species richness. This is accompanied by an increase in beta diversity in extreme age groups, but further defines that this is due to an overall shift of microbial community composition with age, with specific species serving as markers.​

“Overall, these results highlight the value of species-level shotgun metagenomic analysis in large well characterised cohorts, where further studies in other populations would help determine if some of these associations are specific to Asian environments and lifestyles.”​

Source: bioRxiv​

Gut metagenomes of Asian octogenarians reveal metabolic potential expansion and distinct microbial species associated with aging phenotypes​

https://doi.org/10.1101/2024.07.08.602612​

Authors: Aarthi Ravikrishnan, Indrik Wijaya et al​