Electrochemical Investigation of the Role of Reducing Agents in Copper‐Catalyzed Nitric Oxide Release from S‐Nitrosoglutathione

Studies of nitric oxide (NO) release from S ‐nitrosoglutathione (GSNO) decomposition by Cu 2+ in the presence of reducing agents were performed using a nickel porphyrin and Nafion‐coated microsensor in order to compare the efficiency of sodium hydrosulfite (Na 2 S 2 O 4 ) and sodium borohydride (NaBH 4 ) to that of the most abundant endogenous reducer, glutathione (GSH). When it was mixed to Cu(NO 3 ) 2 and added to equimolar concentration of GSNO, each reducing agent caused a NO release (measured in terms of oxidation current) but only NaBH 4 induced a proportional rise if its concentration doubled and that of Cu 2+ remained constant. For Na 2 S 2 O 4 , there was a mild increase and for GSH, no change. Furthermore, when Cu 2+ concentrations ranging from 0.5 to 5 μM were mixed with 2 μM reducing agent and added to 2 μM GSNO , the NO oxidation current linearly increased with NaBH 4 and was constant with Na 2 S 2 O 4 . Concerning GSH, Cu 2+ dose‐dependently increased the NO release from GSNO only if the Cu 2+ ‐to‐reducer ratio was ≤1. However, GSH formed the catalytic species Cu + even in excess of Cu 2+ and GSNO as indicated by suppression of the Cu 2+ /GSH‐induced NO release when the Cu + chelator neocuproine was added to GSNO. This work shows that, among the 3 reducing agents, only NaBH 4 allows Cu 2+ to dose‐dependently increase the NO release from GSNO for Cu 2+ ‐to‐reducer ratios ranging from 0.25 to 2.5. Despite this good effectiveness, excess of NaBH 4 compared to both Cu 2+ and GSNO seems to be required for optimal NO release.