Ozone-Induced DNA Damage: A Pandora’s Box of Oxidatively Modified DNA Bases

Abstract

Ozone is a major component of air pollution and carries potentially mutagenic and harmful affects to health. The oxidation of isolated calf thymus DNA (CT-DNA) led to the nearly quantitative loss of normal DNA 2′-deoxyribonucleosides in the following order: T > G > C ≫ A. The major modification of pyrimidines (T, C, and 5-methylcytosine (5mC)) was the corresponding 5-hydroxyhydantoin derivative after complete digestion of DNA to its component 2′-deoxyribonucleosides. The oxidation of 5mC was 2.5-fold more susceptible than C considering the relative mole fraction of 5mC to C in CT-DNA. Other common oxidation products of pyrimidines (e.g., 5,6dihydroxy-5,6-dihydropyrimidines, the so-called pyrimidine 5,6glycols) were formed with a lower yield than 5-hydroxyhydantoin derivatives. In addition, several common oxidation products of G were observed (e.g., 8-oxo-7,8-dihydroguanine (8oxoG)) albeit with relatively minor yields. The sum of individual products was notably less than the loss of 2′-deoxyribonucleosides from which they were derived. In a search for additional products, we discovered the formation of pyrimidine ring fragments, predominantly Nformamide and N-urea, which were measured as a dinucleotide next to a nonmodified nucleotide upon partial digestion of oxidized DNA. Interestingly, the latter fragments were also observed in dinucleotides containing 8oxoG, indicating the formation of tandem lesions during ozonolysis of DNA. The oxidation of DNA upon exposure to ozone can be explained by reactions of an intermediate ozonide. These studies underline the complexity of ozone-induced DNA damage and provide valuable information to assess the formation of this damage in cellular DNA.

Disinfection efficiency test for contaminated surgical mask by using Ozone generator

“…Moreover, O 3 attacks the sulfhydryl groups of certain enzymes, resulting in disruption of normal cellular enzymatic activity and loss of function. Ozone also attacks the purine and pyrimidine bases of nucleic acids, damaging DNA [ 21 , 22 ]. The advantages of ozone gas are that it reaches shadows and crevices in the process of disinfection, unlike ultraviolet radiation which has a short half-life in an airflow environment.…”

Insights into the 5-Carboxamido-5-Formamido-2-Iminohydantoin Structural Isomerization Equilibria

“…An ozone generator was used to bubble ozone through an aqueous solution contained in a Schlenk flask on ice. The stock concentration of ozone was found using a Beckman UV–vis spectrophotometer based on its molar extinction coefficient at 258 nm of 3.0 × 10 3 M –1 cm –1 . The reaction was initiated by bolus addition of 70 μM ozone to 1.0 mM G buffered with 25 mM NaP i , pH 7.2.…”

“…The stock concentration of ozone was found using a Beckman UV−vis spectrophotometer based on its molar extinction coefficient at 258 nm of 3.0 × 10 3 M −1 cm −1 . 25 The reaction was initiated by bolus addition of 70 μM ozone to 1.0 mM G buffered with 25 mM NaP i , pH 7.2. The mixture was left at 22 °C for 90 min and then lyophilized to dryness.…”

Dynamics of 5R-Tg Base Flipping in DNA Duplexes Based on Simulations─Agreement with Experiments and Beyond

“…Approximately 400 Tg residues are formed in a normal cell each day, and 10–20% of genome damages have been attributed to the oxidative conversion of thymine to Tg. 12 − 18 Due to the chirality of the C5 and C6 atoms, Tg could exist as a mixture of the two pairs of cis - and trans - stereoisomers: the 5R cis–trans pair (5R,6S: 5R,6R) and the 5S cis–trans pair (5S,6R: 5S,6S). 19 − 21 The 5R-Tg stereoisomer is thought to be the more abundant of these, with an equilibrium ratio of 7:3 between cis -5R,6S and trans -5R,6R Tg in DNA oligomers containing the Tg·A base pair, while this ratio is 87:13% at the single-nucleoside level.…”