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. 2010 Apr 26;11(1):2.
doi: 10.1186/1467-4866-11-2.

Adenine oxidation by pyrite-generated hydroxyl radicals

Corey A Cohn  1 , Shawn C Fisher, Bruce J Brownawell, Martin Aa Schoonen
Affiliations

Adenine oxidation by pyrite-generated hydroxyl radicals

Corey A Cohn et al. Geochem Trans. .

Abstract

Cellular exposure to particulate matter with concomitant formation of reactive oxygen species (ROS) and oxidization of biomolecules may lead to negative health outcomes. Evaluating the particle-induced formation of ROS and the oxidation products from reaction of ROS with biomolecules is useful for gaining a mechanistic understanding of particle-induced oxidative stress. Aqueous suspensions of pyrite particles have been shown to form hydroxyl radicals and degrade nucleic acids. Reactions between pyrite-induced hydroxyl radicals and nucleic acid bases, however, remain to be determined. Here, we compared the oxidation of adenine by Fenton-generated (i.e., ferrous iron and hydrogen peroxide) hydroxyl radicals to adenine oxidation by hydroxyl radicals generated in pyrite aqueous suspensions. Results show that adenine oxidizes in the presence of pyrite (without the addition of hydrogen peroxide) and that the rate of oxidation is dependent on the pyrite loading. Adenine oxidation was prevented by addition of either catalase or ethanol to the pyrite/adenine suspensions, which implies that hydrogen peroxide and hydroxyl radicals are causing the adenine oxidation. The adenine oxidation products, 8-oxoadenine and 2-hydroxyadenine, were the same whether hydroxyl radicals were generated by Fenton or pyrite-initiated reactions. Although nucleic acid bases are unlikely to be directly exposed to pyrite particles, the formation of ROS in the vicinity of cells may lead to oxidative stress.

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Figures

Figure 1
Figure 1
(A) Adenine degradation by Fenton-generated hydroxyl radicals. 100 μM adenine was mixed with either Fe(II), H2O2 or a combination of the two, which generates •OH. The solutions were incubated for 24 hrs followed by wavelength scans. Loss of absorbance at 260 nm is indicative of degradation of the adenine molecule. (B) 64 kUnits catalase or 50% ethanol were added to adenine solutions with Fenton reagents. The 1 mM H2O2 & 1 mM Fe(II) plot from graph A is included for comparison. Note that the order in the legend follows the same order of curves in the graphs from top to bottom so in (A), the top three curves overlap (i.e., "nothing added", "1 mM Fe(II)", and "1000 μM H2O2").
Figure 2
Figure 2
Adenine exposed to pyrite. 100 μM adenine was incubated and agitated with 10 g/L pyrite and samples were periodically withdrawn and filtered to remove the pyrite particles before wavelength scans were recorded. In separate vials, 50% EtOH (ethanol) and 64 kUnits catalase were added to pyrite/adenine suspensions.
Figure 3
Figure 3
Adenine exposed to varying pyrite particle loadings (without the addition of hydrogen peroxide). Adenine concentrations were determined by measuring absorbance at 260 nm from filtered samples.
Figure 4
Figure 4
Selected ion chromatographs in negative-ion electrospray for reactions of adenine with Fenton reagents and in presence of pyrite. Two products result from the oxidation of adenine, 2-hydroxyadenine and 8-oxoadenine. Also indicated are the calculated accurate masses of each analyte and the difference when compared with the measured mass of the depronated parent ions.
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