Clostridium butyricum alleviates multiple myeloma by remodeling the bone marrow microenvironment and inhibiting PI3K/AKT pathway through the gut‒bone axis.

MM patients exhibited marked compositional differences in gut microbiota characterized by reduced abundances of butyrate-producing bacteria and diminished butyrate levels compared to healthy individuals.

• Comprehensive microbiome-metabolite analysis was conducted between MM patients and healthy individuals.
• The MM cohort showed reduced abundances of butyrate-producing bacteria.
• Serum/gut butyrate levels were diminished in MM patients compared to healthy controls.
• This finding established a baseline association between gut microbiota dysbiosis and MM.

Fecal microbiota transplantation (FMT) from healthy donors reduced tumor burden in MM and concomitantly elevated serum butyrate levels.

• FMT experiments demonstrated that gut microbiota critically modulates MM progression.
• Healthy donor-derived microbiota reduced the tumor burden in recipient MM models.
• FMT from healthy donors concomitantly elevated serum butyrate levels.
• These results established a causal role of the gut microbiota in MM progression.

Clostridium butyricum was identified as a key butyrate-producing specialist through function-based culturomics screening.

• Function-based culturomics screening was used to identify butyrate-producing bacteria.
• C. butyricum was selected from this screening as a key butyrate-producing specialist.
• This identification guided subsequent probiotic intervention experiments.

C. butyricum or its metabolite butyrate significantly reduced systemic tumor burden in 5TGM1 mice.

• Both C. butyricum and butyrate were tested in 5TGM1 mouse models of multiple myeloma.
• Treatment with C. butyricum significantly reduced systemic tumor burden.
• Treatment with butyrate alone also significantly reduced systemic tumor burden.
• The 5TGM1 mouse model is an established immunocompetent model for MM.

C. butyricum and butyrate alleviated bone marrow inflammation and osteolytic lesions by suppressing Th17 cells and IL-17 levels in the bone marrow.

• C. butyricum and butyrate treatment reduced bone marrow inflammation.
• Osteolytic lesions were alleviated following C. butyricum and butyrate treatment.
• The mechanism involved suppression of Th17 cells in the bone marrow.
• IL-17 levels in the bone marrow were reduced by C. butyricum and butyrate treatment.
• These findings implicate the gut-bone axis as a key pathway for C. butyricum's effects on MM.

Butyrate induced MM cell apoptosis via HDAC inhibition-mediated upregulation of PPARγ, leading to sequential suppression of the PI3K/AKT pathway and antiapoptotic BCL-2 expression.

• Cellular assays and transcriptome sequencing were used to identify the molecular mechanism.
• Butyrate acted as an HDAC inhibitor, upregulating PPARγ expression.
• PPARγ upregulation led to suppression of the PI3K/AKT signaling pathway.
• Suppression of PI3K/AKT led to reduced BCL-2 antiapoptotic expression and subsequent apoptosis.
• This apoptotic signaling cascade was reversed by PPARγ antagonism, confirming PPARγ's central role.

The direct antitumor effect of butyrate-mediated apoptosis was confirmed in M-NSG mice.

• M-NSG mice (immunodeficient humanized myeloma model) were used to confirm direct antitumor effects.
• Results in M-NSG mice corroborated the apoptotic mechanism identified in cellular assays.
• This model allowed assessment of direct tumor cell killing independent of immune modulation.

The study provides the first evidence of immune and molecular mechanisms by which C. butyricum alleviates MM progression, offering preclinical support for probiotic-based therapies.

• The authors describe this as 'the first evidence of the immune and molecular mechanisms by which C. butyricum alleviates MM progression.'
• The study systematically addresses both immune remodeling (Th17/IL-17 suppression) and direct antitumor molecular mechanisms (HDAC/PPARγ/PI3K/AKT/BCL-2).
• The findings provide 'preclinical support for probiotic-based therapies against MM.'
• The research integrates microbiome analysis, FMT, culturomics, in vivo mouse models, and in vitro cellular/transcriptomic approaches.