Iijima Katsunori, Grant Jeanette, McElroy Kenneth, Fyfe Valerie, Preston Tom, McColl Kenneth E L
Department of Gastroenterology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan.
Carcinogenesis. 2003 Dec;24(12):1951-60. doi: 10.1093/carcin/bgg168. Epub 2003 Sep 11.
High luminal concentrations of nitric oxide are generated at the human gastro-oesophaegal junction and within Barrett's oesophagus due to the reduction of salivary nitrite to nitric oxide by acidic gastric juice. Salivary nitrite is derived from the entero-salivary recirculation of dietary nitrate. Our aim was to determine whether nitric oxide generated within the lumen will exert nitrosative stress on the adjacent epithelium. A benchtop model was constructed reproducing the nitrite chemistry occurring within the lumen of the upper gastrointestinal tract where saliva encounters acidic gastric juice. It incorporated an epithelial compartment maintained at pH 7.4 and separated from the lumen by a hydrophobic barrier with the properties of the epithelial lipid cell membrane. The secondary amine morpholine was used to measure N-nitroso compound formation in both the lumen and epithelial compartment. Adding 100 micro M nitrite to the acidic (pH 1.5) luminal compartment depleted of ascorbic acid generated 6.2 +/- 2.0 micro M (mean +/- SE) N-nitrosomorpholine in that compartment and 2.2 +/- 0.1 micro M nitrosomorpholine in the epithelial compartment at 30 min. When 100 micro M nitrite was added to the acidic luminal compartment containing physiological concentrations of ascorbic acid, all the nitrite was immediately converted to nitric oxide and no N-nitrosomorpholine was formed within that compartment. However, the nitric oxide rapidly diffused from the luminal compartment into the epithelial compartment and there generated very high concentrations of N-nitrosomorpholine (137 +/- 5.6 micro M at 30 min). The addition of ascorbic acid or glutathione to the epithelial compartment could only reduce nitric oxide-induced nitrosation within that compartment by 40%. The nitrate-derived nitric oxide generated within the lumen where saliva encounters gastric acid is likely to exert substantial nitrosative stress on the adjacent epithelium. This may contribute to the high prevalence of mutagenesis at this anatomical site.
由于酸性胃液将唾液亚硝酸盐还原为一氧化氮，在人胃食管交界处和巴雷特食管内会产生高腔内浓度的一氧化氮。唾液亚硝酸盐源自饮食硝酸盐的肠-唾液再循环。我们的目的是确定腔内产生的一氧化氮是否会对相邻上皮施加亚硝化应激。构建了一个台式模型，再现了上消化道腔内唾液与酸性胃液相遇时发生的亚硝酸盐化学反应。它包含一个保持在pH 7.4的上皮隔室，通过具有上皮脂质细胞膜特性的疏水屏障与腔分隔开。使用仲胺吗啉来测量腔和上皮隔室内N-亚硝基化合物的形成。在30分钟时，向不含抗坏血酸的酸性（pH 1.5）腔隔室中添加100 μM亚硝酸盐，在该隔室中产生了6.2±2.0 μM（平均值±标准误）的N-亚硝基吗啉，在上皮隔室中产生了2.2±0.1 μM的亚硝基吗啉。当向含有生理浓度抗坏血酸的酸性腔隔室中添加100 μM亚硝酸盐时，所有亚硝酸盐立即转化为一氧化氮，并且在该隔室内未形成N-亚硝基吗啉。然而，一氧化氮迅速从腔隔室扩散到上皮隔室，并在那里产生了非常高浓度的N-亚硝基吗啉（30分钟时为137±5.6 μM）。向上皮隔室中添加抗坏血酸或谷胱甘肽只能将一氧化氮诱导的亚硝化作用在该隔室内降低40%。唾液与胃酸相遇的腔内产生的源自硝酸盐的一氧化氮可能会对相邻上皮施加大量亚硝化应激。这可能导致该解剖部位的诱变高发生率。
