While the molecular weight of nicotinamide riboside is 255.25 g/mol, that of its chloride salt is 290.70 g/mol. As such, 100 mg of nicotinamide riboside chloride provides 88 mg of nicotinamide riboside.
History
Nicotinamide riboside was first described in 1944 as a growth factor, termed Factor V, for Haemophilus influenza, a bacterium that lives in and depends on blood. Factor V, purified from blood, was shown to exist in three forms: NAD+, NMN and NR. NR was the compound that led to the most rapid growth of this bacterium. Notably, H. influenza cannot grow on nicotinic acid, nicotinamide, tryptophan or aspartic acid, which were the previously known precursors of NAD+. In 2000, yeast Sir2 was shown to be an NAD+-dependent protein lysine deacetylase, which led several research groups to probe yeast NAD+ metabolism for genes and enzymes that might regulate lifespan. Biosynthesis of NAD+ in yeast was thought to flow exclusively through NAMN. When NAD+ synthase was deleted from yeast cells, NR permitted yeast cells to grow. Thus, these Dartmouth College investigators proceeded to clone yeast and human nicotinamide riboside kinases and demonstrate the conversion of NR to NMN by nicotinamide riboside kinases in vitro and in vivo. They also demonstrated that NR is a natural product found in cow's milk.
Properties
Although it is a form of vitamin B3, NR exhibits unique properties that distinguish it from the other B3 vitamins—niacin and nicotinamide. In a head-to-head experiment conducted on mice, each of these vitamins exhibited unique effects on the hepatic NAD+ metabolome with unique kinetics, and with NR as the form of B3 that produced the greatest increase in NAD+ at a single timepoint. Different biosynthetic pathways are responsible for converting the different B3 vitamins into NAD+. The enzyme nicotinamide phosphoribosyltransferase catalyzes the rate-limiting step of the two-step pathway converting nicotinamide to NAD+. Two nicotinamide riboside kinases convert NR to NAD+ via a pathway that does not require Nampt. Animal studies have demonstrated that these enzymes respond differently to age and stress. In a mouse model of dilated cardiomyopathy, NRK2 mRNA expression increased, while Nampt mRNA expression decreased. A similar increase in NRK1 and NRK2 expression has been observed in injured central and peripheral neurons. Niacin is known for its tendency to cause an uncomfortable flushing of the skin. This flushing is triggered by the activation of the GPR109AG-protein coupled receptor. NR does not activate this receptor, and has not been shown to cause flushing in humans—even at doses as high as 2,000 mg/day. Despite being an NAD+ precursor, nicotinamide acts as an inhibitor of the NAD+-consuming sirtuin enzymes. When sirtuins consume NAD+, they create nicotinamide and O-acetyl-ADP-ribose as products of the deacetylation reaction. Consistent with high-dose nicotinamide as a sirtuin inhibitor, NR and niacin, but not nicotinamide, have been shown to increase hepatic levels of O-acetyl-ADP-ribose.
Commercialization
In 2004, Dartmouth Medical School researcher Dr. Charles Brenner discovered that NR could be converted to NAD+ via the eukaryotic nicotinamide riboside kinase biosynthetic pathway Dartmouth was subsequently issued patents for nutritional and therapeutic uses of NR, in 2006. ChromaDex licensed these patents in July 2012, and began to develop a commercially viable, full-scale process to bring NR to market. ChomaDex has been in a patent dispute with Elysium Health over the rights to a nicotinamide riboside supplements.
Human clinical testing
There have been five published clinical trials on groups of both men and womentesting for safety. One of these trials studied NR in combination with pterostilbene, while the other four examined the effects of NR alone. The first published clinical trial established the safety and characterized the pharmacokinetics of single doses of NR. Since then, doses as high as 2,000 mg/day have been administered over periods as long as 12 weeks. These studies show that NR can significantly increase levels of NAD+ and some of its associated metabolites in both whole blood and peripheral blood mononuclear cells. In a 12-week clinical trial of obese insulin-resistant men using 2000 mg/day, NR appeared safe, but did not improve insulin sensitivity or whole-body glucose metabolism. In a trial of NR 250 mg plus 50 mg of pterostilbene, as well as with double this dose, the combined supplement raised NAD+ levels in a trial of older adults.
