Determination of nicotinamide N-oxide—a human excretory product

Abstract

A method for the determination of nicotinamide N-oxide has been developed. It is based on the ability of the N-oxide to function as an electron acceptor in the xanthine oxidase catalyzed oxidation of xanthine. In simple mixtures the N-oxide can be converted quantitatively to nicotinamide and the latter determined by the cyanogen bromide method. The conversion is not always quantitative in complex mixtures, such as urine; an isotope dilution variation on the basic method permits the determination of the N-oxide in such situations. The basic method is applicable over the range 0.02–0.3 μmole of nicotinamide N-oxide. The new method has been used to verify the prominent excretory role of nicotinamide N-oxide in rodents. Application of the method to a study of human urines has permitted the detection of the N-oxide as an excretory metabolite in man. Only vanishingly small quantities of the N-oxide are excreted under normal conditions. However after the ingestion of 200 mg of nicotinamide, significant quantities of the N-oxide are detectable in human urine. Urine samples obtained from a number of other mammalian species contained little or no detectable nicotinamide N-oxide.