a Department of Biochemistry , Yanka Kupala State University , Grodno , Belarus.
b Department of Pediatrics , Case Western Reserve University , Cleveland , OH , USA.
Pharm Biol. 2018 Dec;56(1):86-93. doi: 10.1080/13880209.2017.1421674.
Exogenous nitrogen oxides must be made bioavailable to sustain normal physiology because nitric oxide synthase (NOS) deficient mice are viable. In the stomach, S-nitrosoglutathione (GSNO) is formed from ingested nitrite and high levels of airway glutathione (GSH) that are cleared and swallowed. However, gastric GSNO may be broken down by nutrients like ascorbic acid (AA) before it is absorbed.
To study the effect of AA on GSNO formation and stability.
GSH and nitrite were reacted with or without 5 mM AA or Resiston (5 mM AA with retinoic acid and α-tocopherol). GSNO was measured by reduction/chemiluminescence and HPLC. AA and reduced thiols were measured colorimetrically. O-Nitrosoascorbate and AA were measured by gas chromatography-mass spectrometry (GC-MS).
GSNO was formed in saline and gastric samples (pH ∼4.5) from physiological levels of GSH and nitrite. Neither AA nor Resiston decreased [GSNO] at pH >3; rather, they increased [GSNO] (0.12 ± 0.19 μM without AA; 0.42 ± 0.35 μM with AA; and 0.43 ± 0.23 μM with Resiston; n = 4 each; p ≤ 0.05). However, AA compounds decreased [GSNO] at lower pH and with incubation >1 h. Mechanistically, AA, but not dehydroascorbate, increased GSNO formation; and the O-nitrosoascorbate intermediate was formed.
AA, with or without other antioxidants, did not deplete GSNO formed from physiological levels of GSH and nitrite at pH >3. In fact, it favoured GSNO formation, likely through O-nitrosoascorbate. Gastric GSNO could be a NOS-independent source of bioavailable nitrogen oxides.
由于一氧化氮合酶（NOS）缺乏的小鼠能够存活，因此必须使外源性氮氧化物具有生物利用度才能维持正常的生理机能。在胃中，从摄入的亚硝酸盐和被清除和吞下的高气道谷胱甘肽（GSH）中形成 S-亚硝基谷胱甘肽（GSNO）。然而，在被吸收之前，胃中的 GSNO 可能会被像抗坏血酸（AA）这样的营养素分解。
研究 AA 对 GSNO 形成和稳定性的影响。
GSH 和亚硝酸盐在有或没有 5mMAA 或 Resiston（含 5mMAA 的视黄酸和α-生育酚）的情况下反应。通过还原/化学发光和 HPLC 测量 GSNO。通过比色法测量 AA 和还原硫醇。通过气相色谱-质谱联用（GC-MS）测量 O-亚硝基抗坏血酸和 AA。
GSNO 从生理浓度的 GSH 和亚硝酸盐在生理盐水和胃样本（pH 约 4.5）中形成。AA 或 Resiston 在 pH>3 时均不会降低[GSNO]；相反，它们增加了[GSNO]（无 AA 时为 0.12±0.19μM；有 AA 时为 0.42±0.35μM；有 Resiston 时为 0.43±0.23μM；n=4 个；p≤0.05）。然而，在 pH 值较低和孵育时间超过 1 小时时，AA 化合物会降低[GSNO]。从机制上讲，AA 而不是脱氢抗坏血酸增加了 GSNO 的形成；并且形成了 O-亚硝基抗坏血酸中间体。
AA（无论是否有其他抗氧化剂）在 pH>3 时不会耗尽从生理浓度的 GSH 和亚硝酸盐形成的 GSNO。实际上，它有利于 GSNO 的形成，可能是通过 O-亚硝基抗坏血酸。胃中的 GSNO 可能是具有生物利用度的氮氧化物的非 NOS 独立来源。
