Characterizing the Effect of Amylase Inhibitors on Maltodextrin Metabolism by Gut Bacteria Using Fluorescent Glycan Labeling

Abstract

Diet-derived polysaccharides are an important carbon source for gut bacteria and shape the human gut microbiome. Acarbose, a compound used clinically to treat type 2 diabetes, is known to inhibit the growth of some bacteria on starches based on its activity as an inhibitor of α-glucosidases and α-amylases. In contrast to acarbose, montbretin A, a new drug candidate for the treatment of type 2 diabetes, has been reported to be more specific for the inhibition of α-amylase, notably human pancreatic α-amylase. However, the effects of both molecules on glycan metabolism across a larger diversity of human gut bacteria remain to be characterized. Here, we used ex vivo metabolic labeling of a human microbiota sample with fluorescent maltodextrin to identify gut bacteria affected by amylase inhibitors. Metabolic labeling was performed in the presence and absence of amylase inhibitors, and the fluorescently labeled bacteria were identified by fluorescence-activated cell sorting coupled with 16S rDNA amplicon sequencing. We validated the labeling results in cultured isolates and identified four gut bacteria species whose metabolism of maltodextrin is inhibited by acarbose. In contrast, montbretin A slowed the growth of only one species, supporting the fact that it is more selective. Metabolic labeling is a valuable tool to characterize glycan metabolism in microbiota samples and could help understand the untargeted impact of drugs on the human gut microbiota.

Acarbose Impairs GutBacteroidesGrowth by Targeting Intracellular GH97 Enzymes

“…Bacteroides growth inhibition by acarbose has been previously described for Bacteroides thetaiotaomicron (Bt), Bacteroides fragilis (Bf), Phocaeicola dorei , Phocaeicola vulgatus, and B. xylanisolvens (24–26). We extended these data and screened various Bacteroidota species for growth in potato starch and amylopectin with or without 25 µM acarbose ( Fig.…”

“…Since this result was also observed in a particular strain lacking a BoGH13A Sus or SusG homolog, the authors correctly predicted that acarbose inhibits periplasmic Sus enzymes, which we corroborate here coupled with previous data that SusB is inhibited by acarbose (42, 43). The inhibition of periplasmic enzymes and upregulation of sus by acarbose also explains why fluorescent maltodextrin accumulated in the periplasm (26). The authors correctly postulated that buildup of maltooligosaccharides in the periplasm due to enzyme inhibition would lead to more sus upregulation and therefore more maltodextrin transport.…”

“…Lui et al predicted that acarbose targets intracellular enzymes in their work using fluorescently labelled maltodextrin to determine which bacteria are sensitive to acarbose (26). Species that were sensitive to acarbose induced growth inhibition still accumulated fluorescent maltodextrin signal in the periplasm in the presence of acarbose.…”

“…Since acarbose is minimally absorbed by host tissue and transits the gut, one explanation for its gut microbial effects is that it changes bacterial fitness by inhibiting bacterial glucoamylases (22,23). Indeed, preliminary work shows that gut bacterial species are differentially inhibited by acarbose in vitro when grown in starch (24)(25)(26). In particular, members of the prevalent Bacteroidota phylum may be less fit since their relative abundance decreases in acarbose treated individuals (10).…”

“…The Bacteroides do not have homologues to these enzymes which made us question how or if they can circumvent acarbose induced growth inhibition. Recent work demonstrated that some Bacteroides can take up fluorescently labelled maltodextrin in the presence of acarbose even while acarbose impairs growth (26). While this suggests acarbose can target an intracellular enzyme, this has not been shown mechanistically.…”