Prebiotic activity of tart cherry compared to fructooligosaccharides on the gut-bone axis

Abstract

Objectives: Prebiotics are known to have beneficial effects on bone, but their mechanisms of action remain uncertain. Recently, probiotics were reported to modulate the gut-bone axis via the short chain fatty acid (SCFA), butyrate’s effects on regulatory T (Treg) cells. This study investigated how two different prebiotics (i.e. tart cherry [TC] and fructooligosaccharide [FOS]) affect bone cells and whether the response is mediated by Treg cells within the gut-bone axis.

Methods: Eight-week-old C57BL/6 female mice (n=96) were assigned to treatments in 2x3 factorial design with diet (0, 10% TC or 10% FOS) and CD-25 (+CD25 antibody or –CD25 control) as factors. After 8 weeks of treatment, bone structural parameters, biochemical markers, Treg cells in the ileum and bone marrow, fecal SCFAs, and key regulators of bone cell differentiation and activity were assessed. Normally distributed data were analyzed using a 2-way ANOVA; otherwise, Friedman's test was run. For post-hoc analysis Fischer's least square means was used and alpha was 0.05.

Results: As anticipated, the relative abundance of Treg cells in the ileum and bone marrow was suppressed in the groups receiving the CD25 antibody. FOS treatment increased bone mineral content (P <0.01) and density (P <0.05), trabecular bone volume in the vertebra and proximal tibia (P <0.01), and length of the tibia (P <0.01) compared to the control and TC groups. No effect of FOS or TC treatments was observed on the cortical bone. A similar skeletal response was observed in the FOS groups, irrespective of CD25. After 8 wks of treatment, TC increased serum c-terminal end of the telopeptide of type I collagen 1 (CTX-1) compared to control and there was no effect of either prebiotic on procollagen-1 N-terminal peptide (P1NP). FOS increased fecal SCFA (P <0.01) to a greater extent than TC. The relative abundance of mRNA for regulators of osteoblast differentiation (i.e., bone morphogenetic protein 2 [Bmp2] and Osterix), and osteoblast activity (i.e., type 1 collagen [Col1α1]) in the hard tissue of bone were increased with the FOS diet. Likewise, osteocytes were activated as indicated by increased phosphate regulating endopeptidase x-linked (Phex), dentin matrix acidic phosphoprotein 1 (Dmp-1), matrix extracellular phosphoglycoprotein (Mepe) and sclerostin (SOST) gene expression in response to the FOS, but not the TC diets. No changes were noted in osteoclastic genes with either prebiotic. In the ileum, the inflammatory cytokine interleukin-17 (Il17) and T cell trafficking molecules (i.e., C-C motif chemokine receptor 7 [CCR7], C-X-C chemokine receptor type 4 [CXCR4], C-X-C motif chemokine ligand 10 [CXCL10], C-X-C motif chemokine ligand 12 [CXCL12], vascular cell adhesion protein 1 [Vcam1]) decreased in the presence of FOS. All findings support that FOS promotes bone formation.

Conclusion: The findings of this study indicate FOS, but not TC supplementation exerted beneficial effects on bone. This response did not require Treg cells to be present, suggesting that the mechanism through which the prebiotic such as FOS affects bone differs from that of probiotics.