Eduardo Silva

Glucose autoxidation has been proposed as a key reaction associated with deleterious effects induced by hyperglycemia in the eye lens. Little is known about chromophores generated during glucose autoxidation. In this study, we analyzed the effect of oxidative and dicarbonyl stress in the generation of a major chromophore arising from glucose degradation (GDC) and its association with oxidative damage in lens proteins. Glucose (5 mM) was incubated with H₂O₂ (0.5–5 mM), Cu²⁺ (5–50 μM), glyoxal (0.5–5 mM) or methylglyoxal (0.5–5 mM) at pH 7.4, 5% O₂, 37 °C, from 0 to 30 days. GDC concentration increased with incubation time, as well as when incubated in the presence of H₂O₂ and/or Cu²⁺, which were effective even at the lowest concentrations. Dicarbonylic compounds did not increase the levels of GDC during incubations. ¹H, ¹³C and FT-IR spectra from the purified fraction containing the chromophore (detected by UV/vis spectroscopy) showed oxidation products of glucose, including gluconic acid. Lens proteins solutions (10 mg/mL) incubated with glucose (30 mM) presented increased levels of carboxymethyl-lysine and hydrogen peroxide that were associated with GDC increase. Our results suggest a possible use of GDC as a marker of autoxidative reactions occurring during lens proteins glycation induced by glucose.

The fact that proteins are the main target of reactive species formed in the cells and extracellular fluids has led to the realization of a great deal of research devoted to revealing the molecular and biological consequences associated with the presence of intermediary protein radicals. This review article describes and comments upon the main chemical pathways involving primary proteic radicals.

Oxidative modifications of lysozyme (Lyso) and human serum albumin (HSA) mediated by photoinduced processes and peroxyl radicals were studied. Both oxidative conditions were applied to the separate proteins and their mixtures. Dimerization and fragmentation of the proteins do not correlate with the formation of carbonyls or peroxides, implying that evaluation of these changes is not an index of the overall oxidative modification of a protein. The results obtained also show that the hypothesis that the electrostatic interactions of Lyso and HSA could facilitate the formation of Lyso-HSA dimers in the presence of a source of reactive oxygen species was verified in both ROS-producing systems.