Nicotinamide mononucleotide (NMN) deamidation by the gut microbiome and evidence for indirect upregulation of the NAD+ metabolome

Treatment with nicotinamide mononucleotide (NMN) is a prominent strategy to address the age-related decline in nicotinamide adenine dinucleotide (NAD⁺) levels for maintaining aspects of late-life health. It is assumed that exogenous NMN is directly incorporated into NAD⁺ in mammals by the canonical recycling pathway, however the need for NAD⁺ is conserved across evolution, including bacteria in the gut microbiome, which can deamidate NMN to nicotinic acid mononucleotide (NaMN).

Here, we use strategic isotope labelling studies to demonstrate a role for the gut microbiome in deamidating orally delivered NMN into NaMN prior to its uptake and incorporation in mammals. Microbiome depletion increased the overall abundance of NAD metabolites, suggesting a competition relationship. Strikingly, treatment with labelled NMN increased the production of unlabelled NAD precursors, with a greater than 3-fold increase in endogenous NR levels in the gut of antibiotics treated animals upon labelled NMN treatment.

These data suggest that exogenous NMN impacts the NAD metabolome through indirect means, rather than through its direct incorporation, including through the production of endogenous NR via an as-yet unidentified pathway, and demonstrate an important role for the gut microbiome in the assimilation of orally delivered NMN.