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

Ascorbic acid and glutathione (GSH) are important determinants of the intra cellular redox state, and both are known to accelerate the decomposition of S-nitrosoglutathione (GSNO), an endogenous adduct of nitric oxide (NO). Th e implications of these observations for GSNO bioactivity are not yet clear . We investigated the effect of ascorbic acid and GSH on GSNO bioactivity b y using a bioassay with isolated segments of guinea pig aorta suspended in organ chambers. Arterial segments demonstrated relaxation to GSNO (0.1 mu m ol/L) that was significantly enhanced by 300 mu mol/L ascorbic acid (71+/-6 % versus 53+/-6%, P<0.05) but not GSH. Both ascorbic acid and GSH significa ntly shortened the duration of arterial relaxation in response to 0.1 mu mo l/L GSNO (from >120 minutes to 22.5+/-3.5 and 36.3+/-4.3 minutes, respectiv ely; P<0.05), consistent with accelerated decomposition of GSNO that was co nfirmed spectrophotometrical ly. The effect of ascorbic acid was abrogated by either DTPA or the copper(I)-specific agent bathocuproine but not defero xamine, indicating a dependence on the availability of redox-active copper. Consistent with this notion, the action of ascorbic acid on GSNO bioactivi ty was also supported by copper-zinc superoxide dismutase, a physiologicall y relevant source of copper. In contrast, the effect of GSH on GSNO degrada tion and GSNO-mediated arterial relaxation was independent of transition me tal ions, because DTPA had no effect. These data indicate that both ascorbi c acid and GSH modulate GSNO bioactivity and suggest a distinction between the mechanism of GSNO degradation by ascorbic acid or GSH. Whereas both asc orbic acid and GSH accelerate the degradation of GSNO, only ascorbic acid i s dependent on the presence of transition metal ions.