Components of the Gut Microbiome That Influence Bone Tissue-Level Strength

Abstract

Modifications to the constituents of the gut microbiome influence bone density and tissue-level strength, but the specific microbial components that influence tissue-level strength in bone are not known. Here, we selectively modify constituents of the gut microbiota using narrow-spectrum antibiotics to identify components of the microbiome associated with changes in bone mechanical and material properties. Male C57BL/6J mice (4 weeks) were divided into seven groups (n = 7-10/group) and had taxa within the gut microbiome removed through dosing with: (i) ampicillin; (ii) neomycin; (iii) vancomycin; (iv) metronidazole; (v) a cocktail of all four antibiotics together (with zero-calorie sweetener to ensure intake); (vi) zero-calorie sweetener only; or (vii) no additive (untreated) for 12 weeks. Individual antibiotics remove only some taxa from the gut, while the cocktail of all four removes almost all microbes. After accounting for differences in geometry, whole bone strength was reduced in animals with gut microbiome modified by neomycin (-28%, p = 0.002) and was increased in the group in which the gut microbiome was altered by sweetener alone (+39%, p < 0.001). Analysis of the fecal microbiota detected seven lower-ranked taxa differentially abundant in animals with impaired tissue-level strength and 14 differentially abundant taxa associated with increased tissue-level strength. Histological and serum markers of bone turnover and trabecular bone volume per tissue volume (BV/TV) did not differ among groups. These findings demonstrate that modifications to the taxonomic components of the gut microbiome have the potential to decrease or increase tissue-level strength of bone independent of bone quantity and without noticeable changes in bone turnover. © 2021 American Society for Bone and Mineral Research (ASBMR).

Keywords: BIOENGINEERING; BIOMECHANICS; BONE INTERACTORS; BONE MATRIX; ORTHOPEDICS; SYSTEMS BIOLOGY.

© 2021 American Society for Bone and Mineral Research (ASBMR).

Figures

Figure 1:

The study included seven different gut microbiota (six different microbial communities and one cocktail group with a depleted gut microbiota). A) The relative abundance at the phylum level is shown. Each column represents the gut microbiota composition of a single mouse. B) Alpha diversity (Shannon diversity) was decreased in the vancomycin group and increased in the sweetener group. C) Beta diversity (unweighted UniFrac distance), represented in a principal coordinates plot, shows distinct beta diversity among groups. The ellipses represent 95% confidence.

Figure 2:

Removal of components of the gut microbiota using narrow spectrum antibiotics decreased (A) cross-sectional area and (B) section modulus. Mechanical and material properties of bone were influenced by neomycin dosing. (C) Removal of components of the gut microbiota using narrow spectrum antibiotics decreased whole bone strength. (D) A graphical representation of the data and ANCOVA analysis (lines) is shown. Alterations to the gut microbiota caused by dosing with neomycin led to bone strength lower than would be expected from geometry (ANCOVA, p

Figure 3:

Results from linear discriminant analysis (LDA) are shown including cladograms (A,B) and LDA scores (C,D). The cladogram shows different taxonomic ranks represented by rings with phyla in the innermost ring and genera in the outermost ring. Colored circles represent individual taxa and are sized in proportion to relative abundance. Features with an effect size greater than |2| are highlighted. The taxa in each level are colored indicating increased or decreased abundance in (A) impaired bone tissue-level strength (neomycin) or (B) enhanced bone tissue-level strength (sweetener) from that in animals with normal bone strength (untreated, ampicillin, vancomycin, metronidazole, LEfSe analysis confirms that the differences between groups are valid for all subgroups). The corresponding LDA scores are illustrated for p

Figure 4.

A) Predicted functional capacity from PICRUSt results show a decreased abundance in vitamin K biosynthesis in animals with decreased tissue-level strength (dosed with neomycin). Pathways are listed and ordered by ascending p-value. B) Cecal vitamin K content varied among groups. Each color in a column represents the average concentration of phylloquinone (PK) or menaquinone (MK). C) Cecal menaquinone 5 (detection limit 5 pmol/g) and D) cecal menaquinone 6 (detection limit 10 pmol/g) was reduced in the neomycin group when compared to the untreated group. p values for statistical comparisons are indicated for comparisons where p