Radical Acetylation of 2′-Deoxyguanosine and l-Histidine Coupled to the Reaction of Diacetyl with Peroxynitrite in Aerated Medium

Abstract

Diacetyl, like other alpha-dicarbonyl compounds, is reportedly cytotoxic and genotoxic. A food and cigarette contaminant, it is related with alcohol hepatotoxicity and lung disease. Peroxynitrite is a potent oxidant formed in vivo by the diffusion-controlled reaction of the superoxide radical anion with nitric oxide, which is able to form adducts with carbon dioxide and carbonyl compounds. Here, we investigate the nucleophilic addition of peroxynitrite to diacetyl forming acetyl radicals, whose reaction with molecular oxygen leads to acetate. Peroxynitrite is shown to react with diacetyl in phosphate buffer (bell-shaped pH profile with maximum at 7.2) at a very high rate constant ( k 2 = 1.0 x 10 (4) M (-1) s (-1)) when compared with monocarbonyl substrates ( k 2 < 10 (3) M (-1) s (-1)). Phosphate ions (100-500 mM) do not affect the rate of spontaneous peroxynitrite decay, but the H 2PO 4 (-) anion catalyzes the nucleophilic addition of the peroxynitrite anion to diacetyl. The intermediacy of acetyl radicals is suggested by a three-line spectrum ( a N = a H = 0.83 mT) obtained by EPR spin trapping of the reaction mixture with 2-methyl-2-nitrosopropane. The peroxynitrite reaction is accompanied by concentration-dependent oxygen uptake. Stoichiometric amounts of acetate from millimolar amounts of peroxynitrite and diacetyl were obtained under nonlimiting conditions of dissolved oxygen. In the presence of either l-histidine or 2'-deoxyguanosine, the peroxynitrite/diacetyl system afforded the corresponding acetylated molecules identified by HPLC-MS ( n ). These studies provide evidence that the peroxynitrite/diacetyl reaction yields acetyl radicals and raise the hypothesis that protein and DNA nonenzymatic acetylation may occur in cells and be implicated in aging and metabolic disorders in which oxygen and nitrogen reactive species are putatively involved.

Radicals in the reaction between peroxynitrite and uric acid identified by electron spin resonance spectroscopy and liquid chromatography mass spectrometry

“…The diimine 4 is susceptible to nucleophilic addition and can rapidly react with nucleophiles such as water or ammonia [24] and in our case the peroxynitrite anion. The peroxynitrite anion has been reported to undergo nucleophilic addition in many reactions [25–29]. Moreover, both the observed pH dependence and the dependence on CO 2 concentration suggest one important conclusion, which is that the peroxynitrite anion (ONOO − ) is necessary for the production of radicals.…”

“…After undergoing homolysis of the weak peroxo bond (O-O bond) [22,25], the peroxo adduct 5 decomposes to yield nitrogen dioxide ( · NO 2 ) and the radical intermediate 6 , which then rearranges to form a carbonyl radical 7 . The carbonyl radical 7 can be converted to radical 8 by either losing carbon monoxide (CO) or reacting with oxygen (O 2 ) and releasing carbon dioxide (CO 2 ).…”

Reactive Inorganic Oxy‐Species of C, N, S, and P

“…Recently, acetylation of amino acids L-His and L-Lys by acetyl radicals, formed from the reaction of diacetyl and methylglyoxal, has been studied [291,292]. Peroxynitrite reacted with diacetyl and methylglyoxal with second-order rate constants of 1.0 × 10 4 /M/s and 1.0 × 10 3 /M/s, respectively, at pH 7.2 and 25°C.…”

Scientific Opinion on the evaluation of substances as acceptable previous cargoes for edible fats and oils

“…This form of stress has also been linked to diabetes, Alzheimer's disease and cancer (Kovacic and Cooksy, 2005;Massari et al, 2008). This form of stress has also been linked to diabetes, Alzheimer's disease and cancer (Kovacic and Cooksy, 2005;Massari et al, 2008).…”

“…The potential formation of the α-dicarbonyl metabolite from 2,3-butanediol raises the possibility of generation of a reactive carbonyl metabolite that may be both cytotoxic and genotoxic by DNA adduct formation (the so-called carbonyl stress). This form of stress has also been linked to diabetes, Alzheimer's disease and cancer (Kovacic and Cooksy, 2005;Massari et al, 2008). EFSA Journal 2009; 7(11):1391…”