Effect of bedrest on the human gut and oral microbiome: implications for frailty.

Head-down tilt bedrest (HDBR) in older adults caused decreasing gut microbial α-diversity over time in the inactivity group.

• Twenty-two participants aged 55-65 were enrolled in the first Canadian HDBR study conducted in an older cohort.
• Participants underwent fourteen days of HDBR followed by seven days of rehabilitation and additional follow-up appointments.
• Gut taxonomic profiles were generated using V4-V5 16S rRNA gene sequencing from 343 fecal samples.
• The decrease in α-diversity was associated with inactivity conditions during HDBR.

Inactivity during HDBR was associated with decreasing relative abundance of Akkermansia and Lactobacillus in the gut microbiome.

• Both Akkermansia and Lactobacillus are generally considered health-associated gut bacteria.
• These changes were observed specifically in participants assigned to the inactivity group.
• Participants were randomly assigned to either an inactivity or multi-modality exercise intervention group.

Inactivity during HDBR was associated with increasing relative abundance of Bacteroides in the gut microbiome.

• This increase in Bacteroides contrasted with the decreases observed in Akkermansia and Lactobacillus.
• The change occurred in participants in the inactivity group during the fourteen days of HDBR.
• Gut functional profiles were also generated using metagenomic (n=86) data for pathway inference and metabolomic (n=83) data.

Exercise intervention during HDBR was associated with increasing gut relative abundance of Roseburia.

• Roseburia is a butyrate-producing genus generally associated with gut health.
• This increase was observed in participants assigned to the multi-modality exercise intervention group.
• Exercise-associated changes differed from inactivity-associated changes, suggesting exercise may serve as a countermeasure.

Both gut and oral β-diversity were associated with frailty scores and individual frailty components.

• Frailty was measured using a 36-item frailty index.
• Oral taxonomic profiles were generated using V4-V5 16S rRNA gene sequencing from 344 salivary samples.
• The association was found for both gut and oral microbiomes, indicating the relevance of both sites to frailty.
• β-diversity reflects between-sample compositional differences in the microbial community.

The physiological effects of HDBR serve as a model for studying frailty, with inactivity-associated microbiome changes resembling those associated with early frailty development.

• The physiological effects of spaceflight resemble those of ageing and prolonged inactivity.
• Ground-based microgravity analogs such as HDBR have emerged as promising models for studying frailty.
• The study is described as the first Canadian HDBR study conducted in an older cohort (aged 55-65).
• Results may inform strategies to preserve health of older adults facing prolonged inactivity as well as astronauts during space exploration missions.