Variation in ascorbic acid oxidation routes in H2O2 and cupric ion solution as determined by GC/MS

Article abstract of DOI:10.1021/ac00075a006

Recent reports have suggested that ascorbic acid protects low-density lipoprotein from peroxide-induced oxidation, but does not protect and may actually function as a prooxidant in the presence of cupric ions. However, dehydroascorbic acid, (the first oxidation product of ascorbic acid) has been shown to protect low-density lipoprotein from cupric ion oxidation but not peroxide-induced oxidation. We have examined the degradation of ascorbic acid, uniformly labeled [¹³C₆]ascorbic acid, and [6,6-²H₂]ascorbic acid in hydrogen peroxide and cupric ion solutions using gas chromatography/mass spectrometry to determine products and routes of oxidation using different oxidant sources. We have found that hydrogen peroxide leads to the formation of a six-carbon product with a mass increment of 32 (a double oxygen addition) relative to ascorbic acid, consistent with the oxidation sequence of ascorbic acid (mass 176) going to dehydroascorbic acid (mass 174) to 2,3-diketogulonic acid (mass 192) to 2,3-diketo-4,5,5,6-tetrahydroxyhexanoic acid (mass 208). Cupric ion solutions, on the other hand, do not appear to induce significant amounts of 2,3-diketo-4,5,5,6-tetrahydroxyhexanoic acid but rather lead to the formation of a threo-hexa-2,4-dienoic acid lactone (mass 174) as the major six-carbon species. These data suggest that different oxidation stresses lead to solutions containing different ascorbic acid oxidation products. These ascorbic acid-derived species could, in turn, interact differently with other substances in the aqueous environment, including free metal ions and low-density lipoprotein. This may help explain previous reports showing divergent protective effects of ascorbic acid and dehydroascorbic acid on low-density lipoprotein when different oxidation methods are used.