15-deoxy-Δ12,14-prostaglandin J2 stimulates cathepsin-L expression in human pancreatic cancer cells through multiple pathways

Abstract

High concentrations of nitric oxide are generated at the gastroesophageal junction due to the reduction of salivary nitrite to nitric oxide by acidic gastric juice containing ascorbic acid. Salivary nitrite is derived from the enterosalivary recirculation of dietary nitrate and its reduction to nitrite by buccal bacteria. Aims: To determine whether nitric oxide generated in the above way will exert nitrosative stress on the adjacent epithelium. Methods: A benchtop model was constructed reproducing the chemistry occurring at the gastroesophageal junction including a lumen and an adjacent epithelial compartment. The latter was maintained at pH7.4 and separated from the acidic lumen by a thin hydrophobic barrier with the permeability properties of the epithelial cell membrane. The secondary amine morpholine was added to each compartment and N-nitrosomorpholine formation at 15 min measured. Results: Adding 100uM nitrite to the acidic (pill.5) luminal compartment in the absence of ascorbic acid generated 6.2 + 2.0uM (mean + SE) N-nitrosomorpholine in that compartment and 2.2 + O. luM in the adjacent epithelial compartment. When lOOuM nitrite was added to the acidic luminal compartment (pH 1.5) containing ascorbic acid, all the nitrite was immediately converted to nitric oxide and no N-iutrusomorpholine was formed within that compartment. However, the nitric oxide rapidly diffused into the adjacent epithelial compartment (pH 7.4) where it generated very high concentrations of N-nitrosomorpholine (137 + 5.6uM). The concentrations of N-nitrosomorpholine generated in the epithelial compartment decreased with increasing luminal pH being 9SuM at pH2.5, 65uM at pH3.5 and 12uM at pH4.5. The concentration of N-nitrosomorpholine generated in the epithelial compartment was directly related to the nitric oxide concentration in the lumen. The addition of ascorbic acid or ghitathione to the epithelial compartment could only reduce this nitric oxide induced nitrosation within the epithelial compartment by 40%. Conclusion: Ascorbic acid in gastric juice prevents acid-catalysed nitrosation within the gastric lumen. However, in doing so, it generates nitric oxide which exerts a far higher nitrosative stress on the adjacent epithelium. This mechanism is likely to be relevant to the aetiology of mutagenesis and neopfasia at the gastroesophageal junctio