Changes in the gut microbiome and fermentation products concurrent with enhanced longevity in acarbose-treated mice

Abstract

Background: Treatment with the α-glucosidase inhibitor acarbose increases median lifespan by approximately 20% in male mice and 5% in females. This longevity extension differs from dietary restriction based on a number of features, including the relatively small effects on weight and the sex-specificity of the lifespan effect. By inhibiting host digestion, acarbose increases the flux of starch to the lower digestive system, resulting in changes to the gut microbiota and their fermentation products. Given the documented health benefits of short-chain fatty acids (SCFAs), the dominant products of starch fermentation by gut bacteria, this secondary effect of acarbose could contribute to increased longevity in mice. To explore this hypothesis, we compared the fecal microbiome of mice treated with acarbose to control mice at three independent study sites.

Results: Microbial communities and the concentrations of SCFAs in the feces of mice treated with acarbose were notably different from those of control mice. At all three study sites, the bloom of a single bacterial taxon was the most obvious response to acarbose treatment. The blooming populations were classified to the largely uncultured Bacteroidales family Muribaculaceae and were the same taxonomic unit at two of the three sites. Propionate concentrations in feces were consistently elevated in treated mice, while the concentrations of acetate and butyrate reflected a dependence on study site. Across all samples, Muribaculaceae abundance was strongly correlated with propionate and community composition was an important predictor of SCFA concentrations. Cox proportional hazards regression showed that the fecal concentrations of acetate, butyrate, and propionate were, together, predictive of mouse longevity even while controlling for sex, site, and acarbose.

Conclusion: We observed a correlation between fecal SCFAs and lifespan in mice, suggesting a role of the gut microbiota in the longevity-enhancing properties of acarbose. Treatment modulated the taxonomic composition and fermentation products of the gut microbiome, while the site-dependence of the responses illustrate the challenges facing reproducibility and interpretation in microbiome studies. These results motivate future studies exploring manipulation of the gut microbial community and its fermentation products for increased longevity, testing causal roles of SCFAs in the observed effects of acarbose.

Keywords: Acarbose; Candidatus Homeothermaceae; Gut microbiome; Longevity; Muribaculaceae; S24-7; Short-chain fatty acids.

Fig. 1

Survival curves of sampled cohort. Survival curves for mice fed a control diet (blue lines) or mice fed the same diet containing ACA (gold) at each of three sites: TJL, UM, and UT. Median longevity for each group of mice is indicated by a dashed vertical line. Grey circles indicate the age at death for each of the sampled mice at UM and UT. The number of samples summarized by each line is described in Table. 1

Fig. 2

Microbial community composition. Fecal bacterial community composition in mice fed the control diet (circles) or the same diet supplemented with ACA (triangles). The two dominant principal coordinates, based on Bray-Curtis dissimilarities among community profiles, are plotted, and percent of variation explained by each is indicated in parentheses on the axes. The location of points in each panel is identical. Markers denote whether mice were treated (triangles) or controls (circles). In (a) points are colored by treatment: control mice (blue) and ACA-treated (gold), in (b) points are colored by site: TJL (bright pink), UM (blue), and UT (green), and in (c) points are colored by sex: male (light blue) and female (pink). The number of samples depicted in each panel is described in Table 1

Fig. 3

Abundance of dominant OTUs. Relative abundance of the 16S rRNA gene from two OTUs classified as belonging to the family Muribaculaceae, abundant in ACA-treated mice. Points in each panel correspond with samples collected from individual mice at each of three replicate study sites. Samples were obtained from mice fed either the control diet (blue, labeled ‘-’) or the same diet supplemented with ACA (gold, labeled ‘+’). Markers indicate the sex of the mouse: male (triangle) or female (circle). The number of samples illustrated in each panel is described in Table. 1. Boxes span the interquartile range and the internal line indicates the median. (*: P<0.05, **: P<0.001 by Mann-Whitney U test)

Fig. 4

Fecal metabolites. Concentrations of metabolites in feces obtained from mice fed either the control diet (open circles) or the same diet supplemented with ACA (solid circles), at each of three study sites: TJL (bright pink), UM (blue), and UT (green). Lines span the interquartile range and the circle indicates the median. The summed concentration of acetate, butyrate, and propionate is plotted as “total SCFA”. The number of samples summarized in each panel is described in Table. 1. Symbols indicate the significance of a Mann-Whitney U test comparing control to ACA-treated mice. (†:P<0.1,∗:P<0.05,∗∗:P<0.001)

Fig. 5

Microbiota/metabolite correlations. Correlations among metabolite concentrations in feces and family level, spike-adjusted 16S rRNA gene abundances. Points correspond with samples collected from individual mice and colors indicate whether they were obtained from mice fed the control diet (blue) or the same diet supplemented with ACA (gold). Markers indicate the site where the mouse was housed: TJL (diamond), UM (circle), or UT (triangle). Metabolite concentrations are reported normalized to feces wet weight, and abundances are in spike-equivalent units. Values are on a linear scale between 0 and the subsequent tick label, above which, points are plotted logarithmically. The number of samples illustrated in each panel is described in Table 1