Research On The Toxicologic Properties Of Peroxynitrite In Biomimetic Environment Containing Carbon Dioxide

Peroxynitrite （ONOO-） is a powerful oxidizing and nitration agent, which wasgenerated by the combination of nitric oxide （NO） and superoxide （O₂^-） in vivo.Peroxynitrite can oxidize variety classes of biomolecules including lipids, tyrosine,and DNA. However, one of the most abundant constituents of the extracellular milieuis bicarbonate anion （25mM in plasma） which is in equilibrium with carbon dioxide;carbon dioxide can react with peroxynitrite and change the toxicological properties ofperoxynitrite. In this paper we investigated the impact of carbon dioxide on thetoxicological properties of peroxynitrite, three parts was included as following.1. Kinetic research on the reaction of carbon dioxide and peroxynitriteThe rate of peroxynitrite decomposition at physiologically relevant pH andtemperature is¹.0s^-1, which is a first-order reaction. In order to simulate theenvironment in vivo more realistic, the pseudo first order reaction kinetic method wasused to study the reaction kinetics of peroxynitrite with carbon dioxide. At pH7.4,temperature37℃conditions, the rate constant of peroxynitrite and carbon dioxidewas dertermined as k=2.3×10³M^-1s^-1.2. The effects of carbon dioxide on peroxynitrite damage to biomoleculesThe presence of carbon dioxide in the reaction system can inhibit the damage ofperoxynitrite on tryptophan and tyrosine. Using HPLC analysis, in the presence ofcarbon dioxide, the reaction of peroxynitrite and Try or Tyr to generated less nitrationproducts comparing with the reaction system without containing carbon dioxide. Thisindicated that the carbon dioxide can reduce the toxicity of peroxynitrite, becauseperoxynitrite would react with carbon dioxide to produce ONO₂CO₂^-, which thendecompose and yield radicals and modify amino acid again.3. The impact of carbon dioxide on iron porphyrin catalyze peroxynitrite decayThe Stop-Flow instrument was used to study the impact of carbon dioxide oniron porphyrin catalyze peroxynitrite decomposition. The results show that carbondioxide can promote the catalytic action of porphyrin on peroxynitrite decomposition.At physiologically relevant pH and temperature, with or without containing carbondioxide in the system, the catalytic rate constant of porphyrin is1.26×10⁶M^-1s^-1and1.17×10⁶M^-1s^-1, respectively.In this paper, the concentration of bicarbonate in vivo was considered to studythe toxicological properties of peroxynitrite, having positive significance to protectrelated diseases caused by peroxynitrite.