Detection of 3-deoxyfructose and 3-deoxyglucosone in human urine and plasma: evidence for intermediate stages of the Maillard reaction in vivo.

3-Deoxyglucose (3-deoxy-D-erythro-hexos-2-ulose) (3-DG) is a reactive dicarbonyl intermediate involved in the polymerization and browning of proteins by glucose in vitro. Damage to protein by formation of 3-DG in vivo is thought to be limited by enzymes which convert 3-DG to less reactive species, such as 3-deoxyfructose (3-DF). We have developed a sensitive and specific assay for measuring 3-DG and 3-DF in human urine and plasma. In this assay, 3-DG and 3-DF are reduced to 3-deoxy-hexitols (3-DH), using either NaBH4 or NaBD4, and then analyzed by selected ion monitoring gas chromatography-mass spectrometry. Based on comparative analysis of samples reduced with NaBD4 versus NaBD4, 3-DH in urine was derived exclusively (greater than 99%) from 3-DF, while 3-DG accounted for approximately 15% of 3-DH in plasma. The concentrations of 3-DH in fasting human urine and plasma were 5.3 +/- 1.5 micrograms/mg creatinine (n = 18) and 7.2 +/- 1.7 micrograms/dl (n = 18), respectively. The concentrations of 3-DG and 3-DF in plasma (n = 7) were 1.0 +/- 0.2 and 6.7 +/- 1.6 micrograms/dl, respectively. These results suggest that several milligrams of 3-DG are formed in the body per day and detoxified by reduction to 3-DF and support the role of 3-DG as an intermediate in the browning of protein via the Maillard reaction in vivo.