Interaction of 5-aminosalicylic acid with nitrous acid: formation of the diazonium derivative and nitric oxide release C. López-Alarcón, E. Lissi, P. Hoffmann, J. Mella, C.D. Pessoa-Mahana, H. Speisky, M. Möller, G. Ferrer-Sueta, and A. Denicola Abstract: The reaction of 5-aminosalicylic acid (5-ASA) with nitrous acid has been studied at low pH under conditions that simulate a gastric environment. The course of the reaction was followed by UV–visible and fluorescence spectroscopy and the products were analyzed by high performance liquid chromatography (HPLC) with UV–visible and mass spectroscopic detectors. In addition, the formation of nitric oxide (NO) was estimated electrochemically. 5-ASA was readily consumed in a process catalyzed by chloride and thiocyanate, whose rate is first order in 5-ASA and second order in nitrous acid. 2-Hydroxy- 5-diazonium benzoic acid (diazonium derivative) and NO were detected as products of the reaction. From the NO formation profiles, it is concluded that NO is produced as a minor product in a process parallel to the path that leads to generation of the diazonium derivative. While the formation of NO could be beneficial for the protection of the stomach, the generation of the diazonium derivative could be considered a potentially toxic process. Key words: 5-aminosalicylic acid, mesalazine, nitrous acid, nitrite, diazonium derivative, nitric oxide. Résumé : On a étudié la réaction de l’acide 5-aminosalicylique (5-AAS) avec l’acide nitreux, à un pH faible, dans des conditions qui simulent un environnement gastrique. On a suivi l’évolution de la réaction par spectroscopies UV-visible et de fluorescence et on a analysé les produits par chromatographie liquide à haute performance (CLHP) avec des détecteurs par spectroscopie UV-visible et de masse. De plus, on a fait appel à une méthode électrochimique pour évaluer la formation d’ oxyde nitrique (NO). L’acide 5-aminosalicylique est rapidement consommé dans un processus catalysé par les ions chlo- rure et thiocyanate et pour lequel la vitesse est du premier ordre en 5-AAS et du second ordre en acide nitreux. On a détecté de l’acide 2-hydroxy-5-diazoniumbenzoïque (dérivé diazonium) et du NO comme produis de la réaction. D’après les profils de formation du NO, on en conclut que le NO se forme comme produit mineur dans un processus parallèle à la voie qui conduit à la formation du dérivé diazonium. Alors que la formation du NO pourrait être bénéfique pour la protection de l’estomac, la formation du dérivé diazonium peut être considérée comme un processus potentiellement toxique. Mots‐clés : acide 5-aminosalicylique, mésalazine, acide nitreux, nitrite, dérivé diazonium, oxyde nitrique. [Traduit par la Rédaction] Introduction Chronic inflammatory bowel pathologies such as ulcera- tive colitis and Crohn’ s disease cause inflammatory changes and ulcers of different types in the gastrointestinal mucosa. 1 5-Aminosalicylic acid (5-ASA), the active moiety of azosali- cylic drugs such as sulfasalazine and olsalazine, is currently used in the treatment of these pathologies and in the mainte- nance of their clinical remission. 2–4 The mechanism of action of 5-ASA has been related to the inhibition of the production of mediators of the lipooxygenase and cyclo-oxygenase path- ways as well as platelet activating factor, which are elevated in the colonic tissue of patients with inflammatory bowel dis- ease. 4 In addition, 5-ASA inhibits the production of interleu- kin and other cytokines, including tumor necrosis factor alpha. 4 Besides the inhibition of inflammatory pathways, 5-ASA has additional protective effects, being an efficient scavenger of peroxyl radicals and a highly effective molecule in protect- ing membranes against lipid peroxidation. 5–8 Furthermore, after its oxidation by peroxyl radicals, 5-ASA can be regener- ated by endogenous compounds such as ascorbic acid, cys- teine, and glutathione. 9 In addition, 5-ASA delays the Received 9 December 2010. Accepted 4 March 2011. Published at www.nrcresearchpress.com/cjc on XX May 2011. C. López-Alarcón, J. Mella, and C.D. Pessoa-Mahana. Departamento de Farmacia, Facultad de Química, Pontificia Universidad Católica de Chile, C.P. 782 0436, Santiago, Chile. E. Lissi. Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile. P. Hoffmann. UMR/CNRS 5068, Université Paul Sabatier, Toulouse, France. H. Speisky. Instituto de Nutrición y Tecnología de los Alimentos, Universidad de Chile, Santiago, Chile. M. Möller, G. Ferrer-Sueta, and A. Denicola. Laboratorio de Fisicoquímica Biológica, Facultad de Ciencias, and Center for Free Radical and Biomedical Research, Universidad de la República, Montevideo 11400, Uruguay. Corresponding author: C. López-Alarcón (e-mail: clopezr@uc.cl). 628 Can. J. Chem. 89: 628–638 (2011) doi:10.1139/V11-056 Published by NRC Research Press Can. J. Chem. Downloaded from www.nrcresearchpress.com by 190.161.98.148 on 05/04/11 For personal use only.