Vitamin C Degradation Products and Pathways in the Human Lens

Abstract

Vitamin C and its degradation products participate in chemical modifications of proteins in vivo through non-enzymatic glycation (Maillard reaction) and formation of different products called advanced glycation end products. Vitamin C levels are particularly high in selected tissues, such as lens, brain and adrenal gland, and its degradation products can inflict substantial protein damage via formation of advanced glycation end products. However, the pathways of in vivo vitamin C degradation are poorly understood. Here we have determined the levels of vitamin C oxidation and degradation products dehydroascorbic acid, 2,3-diketogulonic acid, 3-deoxythreosone, xylosone, and threosone in the human lens using o-phenylenediamine to trap both free and protein-bound adducts. In the protein-free fraction and water-soluble proteins (WSP), all five listed degradation products were identified. Dehydroascorbic acid, 2,3-diketogulonic acid, and 3-deoxythreosone were the major products in the protein-free fraction, whereas in the WSP, 3-deoxythreosone was the most abundant measured dicarbonyl. In addition, 3-deoxythreosone in WSP showed positive linear correlation with age (p < 0.05). In waterinsoluble proteins, only 3-deoxythreosone and threosone were detected, whereby the level of 3-deoxythreosone was ϳ20 times higher than the level of threosone. The identification of 3-deoxythreosone as the major degradation product bound to human lens proteins provides in vivo evidence for the non-oxidative pathway of dehydroascorbate degradation into erythrulose as a major pathway for vitamin C degradation in vivo.

Extending the Spectrum of α-Dicarbonyl Compounds in Vivo

“…Nemet and Monnier (25) examined the L-threo-ascorbic acid (ASA, vitamin C) degradation products dehydroascorbic acid (DHA), 2,3-diketogulonic acid 2 The abbreviations used are: AGE, advanced glycation end products; ␣-DC, ␣-dicarbonylcompound;ASA,L-threo-ascorbicacid;DHA,dehydroascorbicacid;2,3-DKG, 2,3-diketogulonicacid(L-threo-2,3-hexodiulosonicacid);3-DT,3-deoxythresosone (4-hydroxy-2-oxobutanal); GO, glyoxal; MGO, methylglyoxal (2-oxopropanal); 3-DG,3-deoxyglucosone(3-deoxy-D-erythro-hexos-2-ulose);OPD,o-phenylenediamine; threosone, 3,4-dihydroxy-2-oxobutanal; 1-DG, 1-deoxyglucosone (1-deoxy-D-erythro-hexo-2,3-diulose); DHA, dehydroascorbic acid; DHAP, dihydroxyacetone phosphate; G3P, glyceraldehyde 3-phosphate; 1-DP, 1-deoxypentosone; 3-DP, 3-deoxypentosone; 3,4-DDP, 3,4-dideoxypentosone (3,4-dideoxypentos-2-ulose);1-DT,1-deoxythresosone(1-hydroxy-2,3-butanedione);Q,quinoxaline;HD patients, patients undergoing hemodialysis; 3-DGal, 3-deoxygalactosone; EtOAc, ethyl acetate; 3,4-DGE, 3,4-dideoxyglucosone-3-ene; MeOH, methanol; CID, collision-induced dissociation; glucosone, D-arabino-hexos-2-ulose; Lederer's glucosone, N…”

Multispecificity of Immunoglobulin M Antibodies Raised against Advanced Glycation End Products

“…When used as an antioxidant, vitamin C is readily oxidized to DHA. In addition, DHA can be rearranged into additional degradation products, such as 2,3-diketogulonic acid, 3-deoxythreosone, xylosone, and threosone (6). These vitamin C-derived products can covalently modify proteins through nonenzymatic glycation to generate AGEs (7)(8)(9).…”

Identification of Kynoxazine, a Novel Fluorescent Product of the Reaction between 3-Hydroxykynurenine and Erythrulose in the Human Lens, and Its Role in Protein Modification

“…We did not distinguish between the free and reversibly bound ascorbate degradation products in our assay, unlike in a previous study (16). For DHA-Q, two derivatives were detected, as observed by Henning et al (29).…”

“…Therefore, it is reasonable to assume that 3-DT is mainly generated from 2,3-DKG. Moreover, a previous study demonstrated that 3-DT is the dominant free and proteinbound ␣-dicarbonyl in human lenses (16).…”

“…3-Hydroxykynurenine glucoside (3OHKynG) was synthesized as described previously (28). The quinoxalines of DHA and 2,3-DKG were prepared as described previously (16,29).…”