# Exploratory multi-omics analysis of gut microbiota and fecal metabolites in relation to serum S-equol levels in older adults with osteoporosis from a tropical community: a pilot study

## TL;DR

This pilot study explores how gut bacteria and metabolites relate to S-equol levels in older adults with osteoporosis in a tropical region.

## Contribution

The study is the first to investigate the microbiota-metabolite-S-equol relationship in a tropical osteoporosis population using multi-omics.

## Key findings

- OP participants had lower serum S-equol levels and reduced SCFA-producing gut bacteria compared to controls.
- Metabolomic changes in amino acid and tryptophan pathways were linked to osteoporosis and S-equol levels.
- Certain metabolites showed diagnostic potential for distinguishing OP individuals based on their gut profiles.

## Abstract

Osteoporosis (OP) is a multifactorial skeletal disorder influenced by host metabolism, inflammation, and gut microbiota-derived metabolites such as S-equol. However, the interplay between intestinal microbiota, S-equol production, and host metabolic profiles in OP remains incompletely understood.

To conduct a preliminary multi-omics investigation integrating metagenomic and metabolomic analyses to identify gut microbiota and metabolite biomarkers associated with serum S-equol levels in older adults with OP.

A cross-sectional study was conducted in 39 community-dwelling adults aged ≥50 years in Haikou, China. Participants were grouped into OP and control groups based on lumbar spine T-scores, using a cut-off value of ≤ − 2.5 to define osteoporosis. Serum biomarkers (S-equol, inflammatory cytokines, oxidative stress indicators) were assessed by ELISA. Fecal samples underwent metagenomic sequencing and untargeted metabolomics. LEfSe, Spearman correlation, machine learning, and KEGG enrichment were used to explore microbiota-metabolite-bone health axes.

Serum S-equol levels were significantly lower in the OP group compared to controls (3,561 ± 304 vs. 3,855 ± 469 pg/mL, p = 0.026), whereas most inflammatory markers were comparable between groups, apart from a modest increase in IL-1β in OP. Metagenomic analysis revealed a lower relative abundances of key SCFA-producing taxa in OP (e.g., Faecalibacterium prausnitzii, Roseburia hominis, Bacteroides uniformis). Metabolomic profiling identified distinct alterations in amino acid and tryptophan pathways, with KEGG analysis highlighting disruptions in glycerophospholipid, glycine-serine–threonine, and choline metabolism. Discriminative metabolites (e.g., Gln-Val-Ile-Asp., 5-oxooctanoic acid) showed diagnostic potential (AUC > 0.75). S-equol levels positively correlated with these beneficial microbes and with amino acid-related metabolites (e.g., D-tryptophan, 3-indoleacrylic acid, N-methylglutamate). Network and heatmap analyses illustrated differences in microbial-metabolite association patterns between groups.

In conclusion, low levels of serum S-equol in older adults with osteoporosis were associated with distinct changes in gut microbiota composition and fecal metabolic profiles in this pilot study.