Glucose and ascorbic acid

It should be remembered that some of the established antioxidants have other metabolic roles apart from free-radical scavenging. The finding of reduced antioxidant defences in diabetes, for example, may not be prima fascie evidence of increased oxidative stress, since alternative explanations may operate. For example, this may reflect a response to reduced free-radical activity as su ested by the results of a previous study (Collier et al., 1988). In the case of ascorbate, an alternative explanation has been proposed by Davis etal. (1983), who demonstrated competitive inhibition of ascorbate uptake by glucose into human lymphocytes. This view is supported by the similar molecular structure of glucose and ascorbic acid (see Fig. 12.4) and by a report of an inverse relationship between glycaemic control and ascorbate concentrations in experimental diabetes in rats. Other investigators, however, have not demonstrated this relationship (Som etal., 1981 Sinclair etal., 1991). 

Gutes and coworkers presented an automated electronic tongue based on sequential injection analysis (SIA) and linear sweep voltammetry, for the simultaneous determination of glucose and ascorbic acid, by means of ANN regression. The models were evaluated with an external test set (Gutes et al., 2006). 

Gutes, A., Ibanez, A. B., del Valle, M., and Cespedes, F. (2006). Automated SIA e-tongue employing a voltammetric biosensor array for the simultaneous determination of glucose and ascorbic acid. Electroanalysis 18(1), 82-88. 

Hunt JV, Wolff SP. The role of histidine residues in the nonenzymic covalent attachement of glucose and ascorbic acid to protein. Free Radical Res Commun 1991 14 279-287. 

Matsumoto et al. (1988) coupled enzyme reactors for the elimination of glucose and ascorbic acid with enzyme reactors for the determination of sucrose, glucose and fructose in an FLA manifold. 

Both glucose and ascorbic acid also generate protein-reactive aldehydes and form the oxidizing species mentioned above. Ascorbic acid-derived protein-reactive aldehydes may generate compounds like pentosidine, carboxymethyllysine, and... 

As shown in Fig. 9, ascorbic acid can generate fluorescent products on proteins that are indistinguishable from those produced by glucose on a number of different proteins. Other similarities in glucose and ascorbic acid modification of proteins in vitro also exist. Both glucose and ascorbic acid require close proximity of carbohydrate to protein for protein damage to occur. This is demonstrated in Fig. 10, in... 

FIGURE 13. The reaction between aminoguanidine and products of glucose and ascorbic acid oxidation. The oxidation of ascorbic acid may lead to the formation of a number of aldehydic compounds (a) 3-deoxy-D-erythro-hexose-2-ulose (3-deoxyglucosone), produced by both ascorbic acid and glucose, (b) D-erythro-hexose-2-ulose, (c) D-glycero-pentose-2-ulose. Products (a) and (b) react with aminoguanidine within minutes and compound (c), within hours. An intermediate hydrazone seems likely and leads to the production of triazines. Adapted from Hirsch et al (1992). 

Zhou, Y., T. Nagaoka, F. Li, and G. Zhu. 1999. Evaluation of luminol-H202-KI04 chemiluminescence system and its application to hydrogen peroxide, glucose and ascorbic acid assays. Talanta 48 461-467. 

Matuszewski, W., M. Trojanowicz, and L. Ilcheva. 1990. Simultaneous enzymatic determination of glucose and ascorbic acid using flow-injection amperometry. Electroanalysis 2 147-153. 

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