Protective effects of D-glucaro 1,4-lactone against oxidative/nitrative modifications of plasma proteins

Objective The protective effects of D-glucaro 1,4-lactone (1,4-GL) against oxidative/nitrative protein damage (determined by parameters such as levels of protein carbonyl groups and nitrotyrosine residues) to human plasma treated with peroxynitrite (ONOO−) or hydroperoxide (H2O2) were studied in vitro. We also investigated the effects of 1,4-GL on the level of total free thiol groups and low-molecular-weight thiols (glutathione and homocysteine) in plasma treated with ONOO− (0.1 mM). Methods Levels of carbonyl groups and nitrotyrosine residues in human plasma proteins were measured by ELISA and a competition ELISA, respectively. High-performance liquid chromatography (HPLC) was used to analyze free thiols from plasma. Results Exposure of plasma to ONOO− (0.1 mM) resulted in an increase of the level of carbonyl groups and nitrotyrosine residues in plasma proteins and in a distinct decrease in total thiols and low-molecular-weight thiols (glutathione and homocysteine) measured by high-performance liquid chromatography. In the presence of 1,4-GL (0.4–6.4 mM), a distinct decrease in carbonyl group formation and tyrosine nitration in plasma proteins and changes in plasma thiols caused by 0.1 mM of peroxynitrite were observed. Moreover, 1,4-GL inhibited plasma protein oxidation induced by H2O2 (2 mM). Conclusion The obtained results indicate that in vitro 1,4-GL has inhibitory effects on ONOO−- or hydroperoxide-mediated oxidative stress in human plasma and changes plasma redox thiol status. The mechanism of the antioxidative action of 1,4-GL present in plasma is not known yet.