5-N-Carboxyimino-6-aminopyrimidine-2,4(3H)-dione, a novel indicator for hypochlorite formation

Uric acid is an adequate and endogenous probe for identifying reactive oxygen or nitrogen species generated in vivo because its oxidation products are specific to reacted reactive oxygen or nitrogen species. Recently, we identified 5-N-carboxyimino-6-N-chloroaminopyrimidine-2,4(3H)-dione as a hypochlorite-specific oxidation product. 5-N-carboxyimino-6-N-chloroaminopyrimidine-2,4(3H)-dione was anticipated to be a biomarker for hypochlorite production in vivo. However, while it was stable in aqueous solution at weak acidic and alkaline pH (6.0–8.0), it was unstable ‍in human plasma. In this study, we found that 5-N-carboxyimino-6-N-chloroaminopyrimidine-2,4(3H)-dione rapidly reacted with thiol compounds such as cysteine and glutathione to ‍yield 5-‍N-‍carboxyimino-6-aminopyrimidine-2,4(3H)-dione, which was stable in human plasma unlike 5-N-carboxyimino-6-‍N-‍chloroaminopyrimidine-2,4(3H)-dione. 5-N-carboxyimino-6-aminopyrimidine-2,4(3H)-dione was produced upon uric acid degradation during myeloperoxidase-induced uric acid oxidation and lipopolysaccharide-induced pseudo-inflammation in collected human blood. Therefore, 5-N-carboxyimino-6-aminopyrimidine-2,4(3H)-dione has potential as a marker for hypochlorite produc­tion in vivo.