Characterization of NAD Uptake in Mammalian Cells

Characterization of NAD Uptake in Mammalian Cells

Recent evidence has shown that NAD(P) plays a variety of
roles in cell-signaling processes. Surprisingly, the presence of
NAD(P) utilizing ectoenzymes suggests that NAD(P) is present
extracellularly. Indeed, nanomolar concentrations ofNADhave
been found in plasma and other body fluids. Although very high
concentrations of NAD have been shown to enter cells, it is not
known whether lower, more physiological concentrations are
able to be taken up. Here we show that two mammalian cell types
are able to transport low NAD concentrations effectively. Furthermore,
extracellular application ofNADwas able to counteract
FK866-induced cell death and restore intracellular NAD(P)
levels. We propose that NAD uptake may play a role in physiological
NAD homeostasis…

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