Figure 3. SNOAC is formed from NAC in blood ex vivo and in vivo.

(A) The SNO_rbc in heparinized LV blood (black bars), measured by reductive chemiluminescence (11), was lower than normal following 3 weeks of treatment with 10 mg/ml NAC (n = 3–4 each). In the same mice, plasma SNOAC levels (gray bars; measured by MS) increased from undetectable to approximately 2 μM over the same time (*P < 0.05). (B) Serum SNOAC, measured by MS, formed in NAC-treated mice (3 weeks). Left: liquid chromatogram; right: MS spectrum. NAC-treated mice had a SNOAC peak (m/z 193; red) coeluting with ¹⁵N-labeled SNOAC standard (m/z 194; black) that was absent in untreated animals (green) and was not detected in NAC-treated mice after serum pretreatment with HgCl₂ to displace NO⁺ from the thiolate (blue). (C) Oxygenated erythrocytes were deoxygenated ex vivo (argon; ref. 11) in the presence of 100 μM NAC; supernatant SNOAC was measured by MS (above). SNOAC concentration increased with oxyhemoglobin (Oxy Hb) desaturation (co-oximetry: inset), being maximal at 59.3% saturation (blue), less at 77.2% saturation (green), and undetectable at 98% saturation. (D) SNOAC (filled circles) accumulated as the concentration of S-nitrosothiol–modified Hb (SNOHb; open circles) and oxyhemoglobin saturation (Hb SO₂; blue line) both decreased in heparinized whole blood using argon with 5% CO₂ (pH 7.3) in a tonometer. Both the increase in SNOAC and the loss of SNO_rbc between 0 and 20 minutes were significant (P < 0.01 by ANOVA followed by pairwise comparison to the maximum value; n = 3). ^#SNOAC levels were below the limit of detection when the oxyhemoglobin saturation was greater than 80%.