Compared with BP group, 23 metabolites were significantly altered in SD group: creatinine, azelaic acid, protocatechuic acid, and 3,4-dihydroxyhydrocinnamic acid were upregulated, yet lactate, glycolic acid, alanine, nicotinic acid, phenylacetic acid, glycine, 4-deoxyerythronic acid, pipecolic acid, 2,4-dihydroxybutanoic acid, nicotinamide, uracil, threonic acid
, suberic acid, putrescine, citric acid, hippurate, lysine, urate, and ascorbic acid were downregulated in SD group as shown in the heat map (Figure 5(a)).
is an oxidation product of ascorbic acid and increased when plasma was incubated for a prolonged time (Fig.
In addition, DHA and 2,3-diketogulonic acid may also be further oxidized by molecular oxygen, [H.sub.2][O.sub.2], and some metal oxyanions (permanganate, chromate) to products such as threonic acid
, oxalic acid, and various smaller products (e.g., carbon dioxide) that cannot be reverted back to ascorbic acid (Deutsch 1998).
Statistical analysis revealed that the concentration of 2,3,4-trihydroxybutanoic acid (threonic acid) detected by GC-MS (Fig.
Metabolomics revealed increased concentrations of threonic acid after storage at room temperature.
The observed increase in threonic acid over time, however, indicates that oxygen-sensitive metabolites require specific protective measures during sample preparation and storage.
The degradation of DKG produces threonic acid (19), which also has a molecular mass of 136 (Fig.
The second aim was to differentiate molecule-136 from threonic acid. The third aim was to propose a chemical structure for molecules-136 and -208.
To test whether molecule-136 is different from threonic acid, we compared fragmentation spectra of commercial threonic acid (Aldrich) and molecule-136.
Tandem MS was performed on an Agilent ion-trap mass analyzer to compare the fragmentation spectrum of threonic acid with that of molecule-136 produced from the mixtures of AA and riboflavin exposed to ambient light for 24 h.