NRK1 controls nicotinamide mononucleotide and nicotinamide riboside metabolism in mammalian cells.
Level 5 - mechanism / opinion, no new human data
Mechanistic in vitro bench research and genetic models without human data.
PubMed 27725675 · doi:10.1038/ncomms13103
What was done
The authors investigated how mammalian cells utilize exogenous NAD+ precursors including nicotinamide mononucleotide (NMN), nicotinamide riboside (NR), nicotinamide, and nicotinic acid. Using genetic gain- and loss-of-function mammalian cell models targeting nicotinamide riboside kinase 1 (NRK1) alongside stable isotope-labelled tracer compounds, they evaluated cellular uptake mechanisms and metabolic pathways leading to NAD+ synthesis.
What was found
NRK1 was necessary and rate-limiting for the utilization of exogenous NR and NMN in NAD+ synthesis, while remaining dispensable for synthesis from nicotinamide or nicotinic acid. Isotope-labelling confirmed that extracellular NMN is metabolized extracellularly to NR prior to cellular uptake and subsequent conversion to NAD+. The abstract reports no numerical values, effect sizes, or kinetic metrics.
Why it matters
This study clarifies the cellular entry pathway of NMN, demonstrating that extracellular NMN is converted to NR before transport, which explains why both precursors produce overlapping metabolic effects in mammals.
Limits
All reported findings come from preclinical in vitro cell and genetic models with no human in vivo data. The abstract reports no sample sizes, effect sizes, or statistical metrics, and findings may not account for tissue-specific variation in transporter expression.
Cited by
- supports Research indicates that nicotinamide riboside (NR) converts to NAD+ within cells more readily than nicotinamide mononucleotide (NMN).