The faecal microbiota composition of the various mouse groups were compared by sequencing their 16S ribosomal RNA gene.
Results showed that the mice that had been drinking saccharin had a distinct microbiota composition that clustered separately from both their starting microbiome, and from that of the control groups. Similarly, the microbiome of the faecal recipients of saccharin-drinking mice showed a separate clustering compared to the recipients of the glucose-drinkers. Overall, a similar configuration of dysbiosis (bacterial imbalance) was observed in all mice groups that consumed saccharin compared to all control groups.
The functional changes of the microbiota after NAS exposure were studied by performing shotgun metagenomic sequencing on the faecal samples before saccharin consumption, and after eleven weeks of treatment. Comparison of relative species abundance was done by mapping sequencing reads to the human microbiome project reference genome database.
The results showed that saccharin treatment induced large chances in microbial relative species abundance.
Mapping of metagenomic reads to a gut microbial gene catalogue also showed a change in the abundance of pathways in saccharin-consuming mice compared to their control counterparts. Over-represented pathways in saccharin-drinking mice included glycan degradation pathways, marking enhanced energy harvest which may be associated with obesity in mice and humans. This is due to fermentation of glycans into various compounds, including short-chain fatty acids (SCFAs), which may serve as precursors and/or signalling molecules for de novo synthesis of glucose or lipids in the host.
The increase in these pathways is attributable to reads originating from the same bacteria that were found to be abundant in saccharin-consuming mice. This was consistent with the sharp increase in the abundance of particular genera observed in 16S rRNA analysis of NAS-consuming mice.
Other pathways were also enriched in microbiomes of the NAS-consuming mice, including:
- Starch, sucrose, fructose and mannose metabolism
- Folate, glycerolipid and fatty acid biosynthesis
The glucose transport pathways were decreased by comparison.
In HFD-fed mice with saccharin intake, other pathways were also enriched, including:
- Ascorbate and aldarate metabolism – reportedly enriched in leptin-receptor-deficient diabetic mice
- Lipopolysaccharide biosynthesis – linked to metabolic endotoxaemia
- Bacterial chemotaxis – reportedly enriched in obese mice
Reference: Suez, Jotham et al. ‘Artificial Sweeteners Induce Glucose Intolerance By Altering The Gut Microbiota’. Nature (2014)