Adenine oxidation by pyrite-generated hydroxyl radicals

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.

Role of hydrogen peroxide and hydroxyl radical in pyrite oxidation by molecular oxygen

“…5. In an air-saturated pyrite suspension, adenine degrades, consistent with our earlier results Cohn et al, 2010). However, if ferric iron is the oxidant, there is little or no adenine degradation.…”

“…Adenine is stable in the presence of hydrogen peroxide ), but will convert to 8-oxoadenine and 2-hydroxyadenine (isoguanine) when reacting with hydroxyl radical (Cohn et al, 2010). Hence, adenine degradation in pyrite slurries is an indirect probe recording the formation of hydroxyl radicals.…”

“…The near-absence of oxygen in the atmosphere would have preserved pyrite exposed in various types of rock and erosion would have transported pyrite as detrital grains and deposited them in deltas. Oxidation of this detrital pyrite may have given rise to hydroxyl radicals, which could have stressed emerging biological systems by damaging cell membranes, nucleic acids, and proteins (Imlay, 2003;Cohn et al, 2004Cohn et al, , 2006Cohn et al, , 2010. The environmental stress may have led to the selection of those organisms that had developed strategies to minimize damage by hydrogen peroxide and its reaction product, hydroxyl radical.…”

Antioxidant and Anti-Apoptotic Activity of Vasoactive Intestinal Peptide (VIP) Against 6-Hydroxy Dopamine Toxicity in the Rat Corpus Striatum

“…In both cases, it is possible that neither the activity of CAT nor the concentration of its reactive species, hydrogen peroxide, is increased in the brain tissue. Hydroxyl radicals are reported to be very potent for adenine oxidation and DNA damage, and they are also the primary cause of lipid peroxidation (Cohn et al 2010). In this study, increased MDA and DNA fragmentation were indicative of oxidative stress and apoptosis in response to 6-OHDA toxicity.…”

An improved pyrite pretreatment protocol for kinetic and isotopic studies

“…Due to its diverse roles in the natural and anthropogenic sulfur cycle, pyrite has been extensively studied in various experimental investigations of the kinetics of its dissolution and oxidation [9][10][11][12][13][14][15][16], the isotopic fractionations associated with these reactions [17][18][19][20][21][22], the microbiological processes involved [23][24][25], and the effect of pyrite surface reactivity and hydroxyl radical formation on human health [26][27][28][29]. Common to many of these studies is the pretreatment of pyrite to prevent experimental artifacts and inaccuracies.…”