# Periodontitis-associated salivary microbiota exacerbates systemic osteoclastogenesis via gut modulation and tryptophan metabolism suppression in ovariectomized mice

## TL;DR

Periodontitis-related bacteria in saliva worsen bone loss in mice by altering gut bacteria and reducing tryptophan metabolism, but adding a specific tryptophan metabolite can help reverse this effect.

## Contribution

This study identifies a novel oral-gut axis mechanism linking periodontitis to systemic bone loss and proposes ILA supplementation as a potential treatment.

## Key findings

- Periodontitis patients have more diverse and pathogenic salivary microbiota compared to healthy individuals.
- Salivary microbiota from periodontitis patients modulates gut microbiota and suppresses tryptophan metabolism in ovariectomized mice.
- Supplementing with indole-3-lactic acid (ILA) reduces bone destruction caused by periodontitis-associated microbiota.

## Abstract

Epidemiological studies have highlighted an association between periodontitis and osteoporosis. However, the mechanism underlining this association remains unclear. Here, we revealed significant differences in the salivary microbiota between periodontally healthy individuals and periodontitis patients, with periodontitis patients exhibiting increased salivary microbiota diversity and an elevated abundance of pathogenic bacteria. Using an ovariectomized (OVX) mouse model, we demonstrated that the salivary microbiota from periodontitis patients exacerbated bone destruction by modulating the gut microbiota. Metabolomic analysis revealed that the periodontitis-associated salivary microbiota suppressed tryptophan metabolism. The tryptophan metabolite indole-3-lactic acid (ILA) directly inhibited osteoclast formation and differentiation. In OVX mice treated with periodontitis salivary microbiota, supplementation with ILA effectively suppressed osteoclastogenesis and alleviated the detrimental effects of periodontitis-associated salivary microbiota on systemic bones. In summary, our data demonstrate that periodontitis can affect systemic bone metabolism via the oral–gut axis and that ILA supplementation serves as a potential therapeutic option to mitigate these adverse effects.