Abstract

The use of N-methylnicotinamide (NMN) as a biomarker for nitrate/nitrite exposure was investigated in three rat experiments and one human study with volunteers. Rats have been exposed to 36 mmol KCl, KNO2 or KNO3 per liter tap water for 2, 12 and 13 weeks. In general, the animals receiving KNO2 showed a statistically significant (p<0.01) twofold increase in NMN compared with the KCl-group. This increase was observed after a relatively high exposure (about 800 mg/kg body weight/day). The induction of urinary NMN in humans was investigated in an experiment with 8 human volunteers who received a single oral dose of sodium nitrate, corresponding with 10 mg NaNO3/kg b.w./day (2 times the acceptable daily intake for nitrate). After the single dose of sodium nitrate a rapid increase of urinary NMN (up to six-fold) was observed in four volunteers. In the other four volunteers the urinary NMN concentration did hardly react. When the same experiment was repeated with the same volunteers, it was remarkable to see that all volunteers showed the same response on urinary NMN as in the first experiment. It is concluded that NMN can possibly be a good biomarker for the internal nitrite exposure of humans but further studies are nessecary to assess its value.