title: Protection against peroxynitrite-induced DNA damage by mesalamine: implications for anti-inflammation and anti-cancer activity.
abstract: Mesalamine (5-aminosalicylic acid, 5-ASA) is known to be the first-line medication for treatment of patients with ulcerative colitis. Studies have demonstrated that ulcerative colitis patients treated with 5-ASA have an overall decrease in the risk of developing colorectal carcinoma. However, the mechanisms underlying 5-ASA-mediated anti-inflammatory and anti-cancer effects are yet to be elucidated. Because peroxynitrite has been critically involved in inflammatory stress and carcinogenesis, this study was undertaken to investigate the effects of 5-ASA in peroxynitrite-induced DNA strand breaks, an important event leading to peroxynitrite-elicited cytotoxicity. Incubation of φX-174 plasmid DNA with the peroxynitrite generator 3-morpholinosydnonimine (SIN-1) led to the formation of both single- and double-stranded DNA breaks in a concentration-dependent manner. The presence of 5-ASA at 0.1 and 1.0 mM was found to significantly inhibit SIN-1-induced DNA strand breaks in a concentration-dependent manner. The consumption of oxygen induced by SIN-1 was found to not be affected by 5-ASA at 0.1-50 mM, indicating that 5-ASA at these concentrations is not involved in the auto-oxidation of SIN-1 to form peroxynitrite. It is observed that 5-ASA at 0.1-1 mM showed considerable inhibition of peroxynitrite-mediated luminol chemiluminescence in a dose-dependent fashion, suggesting that 5-ASA is able to directly scavenge the peroxynitrite. Electron paramagnetic resonance (EPR) spectroscopy in combination with spin-trapping experiments, using 5,5-dimethylpyrroline-N-oxide (DMPO) as spin trap resulting in the formation of DMPO-hydroxyl radical adduct from peroxynitrite, and 5-ASA only at higher concentration (1 mM) inhibited the hydroxyl radical adduct while shifting EPR spectra, indicating that 5-ASA at higher concentrations may generate a more stable free radical species rather than acting purely as a hydroxyl radical scavenger. Taken together, these studies demonstrate for the first time that 5-ASA can potently inhibit peroxynitrite-mediated DNA strand breakage, scavenge peroxynitrite, and affect peroxynitrite-mediated radical formation, which may be responsible, at least partially, for its anti-inflammatory and anti-cancer effects.
authors.affiliation: Division of Biomedical Sciences, Edward Via College of Osteopathic Medicine, Blacksburg, VA 24060, USA.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Graham
authors.forename: Jason Z
authors.initials: JZ
authors.lastname: Li
authors.forename: Xueging
authors.initials: X
authors.lastname: Dou
authors.forename: Hong
authors.initials: H
authors.lastname: Zhu
authors.forename: Hara P
authors.initials: HP
authors.lastname: Misra
authors.forename: Zhenquan
authors.initials: Z
authors.lastname: Jia
authors.forename: Yunbo
authors.initials: Y
authors.lastname: Li
mesh_terms: D000893:Anti-Inflammatory Agents / Q000737:chemistry*; D016588:Anticarcinogenic Agents / Q000737:chemistry*; D010584:Bacteriophage phi X 174 / Q000235:genetics; D003093:Colitis, Ulcerative / Q000150:complications / Q000188:drug therapy; D015179:Colorectal Neoplasms / Q000209:etiology / Q000517:prevention & control; D053903:DNA Breaks, Double-Stranded; D053904:DNA Breaks, Single-Stranded; D004279:DNA, Viral / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D016166:Free Radical Scavengers / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry*; D006801:Humans; D019804:Mesalamine / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D030421:Peroxynitrous Acid / Q000737:chemistry*; D010957:Plasmids / Q000235:genetics
chemical_list: D000893:Anti-Inflammatory Agents; D016588:Anticarcinogenic Agents; D004279:DNA, Viral; D016166:Free Radical Scavengers; D005609:Free Radicals; D030421:Peroxynitrous Acid; D019804:Mesalamine; D010100:Oxygen