How does SLC12A8 work? Once NMN is in circulation, how does it get into the cells?
The first study on it showed SLC12A8 was most highly expressed in the intestine. But is elsewhere, such as liver.
This article reviews a second study that found SLC12a8 in liver cells does transport NMN. It also found SLC12A8 was upregulated when cells are low in NAD+, and totally shut down when cells have sufficient NAD+. Strong confirmation of SLC12A8 for NMN import in some cells other than intestine. Might also explain why the initial study found SLC12A8 in few tissues, if it is upregulated when cells are more in need.
Sublingual will deliver up to 30% to blood. The remainder will go through the GI tract.
Liposomal delivery will bypass the GI tract almost completely, so a much higher % makes it to the bloodstream intact.
However, the 70+% of NMN that goes through the GI tract, much will be digested by bacteria to NaMN and take a different path to NAD+. Unknown how efficient that is compared to delivering NMN direct to the bloodstream.