Probiotic Supplementation Enhances Functional Recovery and Modulates the Serum Metabolome in Mice

Bone fractures represent common traumatic injuries associated with significant morbidity due to acute and, in some cases, persistent chronic pain. Emerging evidence suggests the gut microbiota plays a critical role in modulating inflammatory and nociceptive signaling; however, its potential as a therapeutic target for alleviating fracture-related pain remains largely unexplored. In this study, we examined the effects of probiotic supplementation with Bifidobacterium longum (B. longum) or Lacticaseibacillus casei (L. casei) on pain-related behaviors, functional recovery, and systemic metabolic changes after unilateral femoral fracture in female C57BL/6J mice. While probiotic supplementation did not significantly alter body composition or whole-body bone mineral density, B. longum supplementation resulted in a modest but significant increase in lumbar spine bone mineral density. Both probiotic strains significantly attenuated pain behaviors compared to vehicle-treated controls, with B. longum demonstrating more rapid and pronounced analgesic effects, including improved hindlimb gait symmetry and reduced compensatory limb usage. Untargeted metabolomic analysis revealed strain-specific and time-dependent changes in systemic metabolic profiles, notably affecting pathways involved in neurotransmitter biosynthesis, tryptophan metabolism, and inflammatory signaling. Collectively, these findings highlight the therapeutic potential of microbiota-targeted strategies as nonpharmacological interventions for improving functional recovery and reducing pain behavior following traumatic bone injury.