Ascorbic acid and glutathione modulate the biological activity of S-nitrosoglutathione

Ascorbic acid and glutathione (GSH) are important determinants of the intracellular redox state, and both are known to accelerate the decomposition of S-nitrosoglutathione (GSNO), an endogenous adduct of nitric oxide (NO). The implications of these observations for GSNO bioactivity are not yet clear. We investigated the effect of ascorbic acid and GSH on GSNO bioactivity by using a bioassay with isolated segments of guinea pig aorta suspended in organ chambers. Arterial segments demonstrated relaxation to GSNO (0.1 micromol/L) that was significantly enhanced by 300 micromol/L ascorbic acid (71+/-6% versus 53+/-6%, P<0.05) but not GSH. Both ascorbic acid and GSH significantly shortened the duration of arterial relaxation in response to 0.1 micromol/L GSNO (from >120 minutes to 22.5+/-3.5 and 36.3+/-4.3 minutes, respectively; P<0.05), consistent with accelerated decomposition of GSNO that was confirmed spectrophotometrically. The effect of ascorbic acid was abrogated by either DTPA or the copper(I)-specific agent bathocuproine but not deferoxamine, indicating a dependence on the availability of redox-active copper. Consistent with this notion, the action of ascorbic acid on GSNO bioactivity was also supported by copper-zinc superoxide dismutase, a physiologically relevant source of copper. In contrast, the effect of GSH on GSNO degradation and GSNO-mediated arterial relaxation was independent of transition metal ions, because DTPA had no effect. These data indicate that both ascorbic acid and GSH modulate GSNO bioactivity and suggest a distinction between the mechanism of GSNO degradation by ascorbic acid or GSH. Whereas both ascorbic acid and GSH accelerate the degradation of GSNO, only ascorbic acid is dependent on the presence of transition metal ions.