Chelation of Cellular Cu(I) Raised the Degree of Glyoxalase I Inactivation in Human Endothelial Cells upon Exposure to S-Nitrosoglutathione through Stabilization of S-Nitrosothiols.

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Abstract
This study aimed to examine molecular mechanisms responsible for the metabolic fate of S-nitrosoglutathione (GSNO) in endothelial cells. After addition of 1 mM GSNO in culture medium, concentration of S-nitrosothiols (RSNO) significantly decreased with concomitant accumulation of nitrite (NO2-) only in the presence of human endothelial cells (ECV304), while no change in RSNO decomposition and NO2- accumulation was observed in case of S-nitrosocysteine. Bathocuproine disulfonic acid (BCS), a chelator for Cu(I), prevented the cell-mediated decomposition of RSNO and accumulation of NO2-. Chelator for Cu(II), Fe(II), or Fe(III); inhibitors of γ-glutamyltranspeptidase; or a superoxide quenching enzyme had no effect on the cell-mediated degradation of RSNO and accumulation of NO2-. These results indicate that cellular Cu(I) would play a major role in the conversion of GSNO into NO2-. We recently demonstrated that human glyoxalase I (Glo I) interacts with GSNO in vitro and within cells. When Glo I interacts with GSNO, Glo I is inactivated and is chemically modified with pI alteration on 2D gels. So, we examined effect of Cu(I) chelation on the Glo I response. As a result, chelation of cellular Cu(I) by BCS enhanced the inactivation and chemical modification of Glo I by GSNO. The Glo I response could be detected when the cells were exposed to GSNO at 10 μM, corresponding to the concentration of RSNO under physiological conditions, with pretreatment of BCS. Metal chelators for copper and iron ions had no effect on the sensitivity of Glo I to an nitric oxide (NO) radical donor. These results indicate that chelation of cellular Cu(I) potentiates the sensitivity of Glo I to GSNO. The observation in the present study implicates that intracellular levels of GSNO might be elevated, accompanying with stabilization of extracellular RSNO.